Non-Jewish Prostitutes - Torah & Rabbinic prohibitions

shoshi asked in a previous post:

Someone who spent more than 10 years learning in a kollel told me that "there is no issur mideoraita to have sexual intercourse with a non-jewish woman, as long as no one sees it"

He says that only Rambam says that there is an issur mideoraita, but if you do not accept rambam, you can go with non-jewish prostitutes as a religious jew and you do not infringe halacha, except perhaps miderabbanan.

Can you confirm this opinion?
If not: what are the sources?

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To summarize the answer. Contrary what your "former kollel member" told you, it is prohibited on the Doreissa level according to many poskim. Rambam's position is not clear - except he emphasizes that the prohibition in private is rabbinic - but leaves open the question whether the person incurs kares (from tradition). In other words he holds that the Torah prohibitions of "Not to marry non-Jews" and "the zealots can kill them" only applies to public acts or marriage. but possibly holds that private acts are punished by kares (from tradition) which is not a rabbinic punishment but similar to a Torah punishment. On the other hand there are clearly views that do accept that the prohibition is entirely rabbinic and that there is no kares for private acts. It is not clear what the majority position is. Furthemore to say that "you do not infringe halacha, except perhaps miderabbanan" shows a gross ignorance or insensitivity to not only the nature of rabbinic prohibitions but also the seriousness that they - the divinely prescribed guardians and shapers of Judaism - view that matter. Therefore anyone who has any concern for his soul would not engage in such behavior.
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Regarding the question raised as to the prohibition of non-Jewish prostitutes. Here are some sources I have gathered. There is more material - but this should suffice to show that it is not simply a decree made by some rabbis 2000 years ago- but it also involves a Torah prohbition as well as being punishable by kares (known from tradition). The Rabbinic prohibitions are extensively discussed details in Avoda Zara (36b) and Sanhedrin (82a). It doesn't take a great talmid chachom to understand that the matter is viewed as a serious transgression.

Rambam (Hilchos Issurei Bi’ah 12:2): There is only an explicit Torah prohibition of sexual relations with non‑Jews in the context of marriage. However if one fornicated with a non‑Jewess in the manner of zenus – then there is a rabbinical punishment of lashes which was made as a decree to prevent intermarriage. If he had a regular relationship without marrying her than he transgresses the prohibitions of nidda, maidservant, relationship with a non‑Jewess and because of prostitution. If they didn’t have a regular relationship than he is only liable because of relationship with a non‑Jewesss. All these liablities are rabbinic.

Rambam (Hilchos Issurei Bi’ah 12:6): If the man having relations with a non-Jewish woman doesn’t get punished by zealots and doesn’t get lashes from beis din – then the punishment is kares which is known from tradition (Malachi 2:11-12)…We learn from this verse that someone who has sexual relations with a non‑Jewish woman is as if he is married to an idol since this verse describes her the daughter of a strange god and it is described as profaning G‑d’s holiness.

Shulchan Aruch (E.H. 16:1): A Jew who has sexual relations with a non‑Jew in the context of marriage or a Jewish woman who has sexual relations with a non‑Jew receive lashes according to Torah as it says in Devarim (7:3). Others disagree. However some who has sexual relations with a non‑Jew not in the context of marriage and not in a fixed relationship receives lashes according to Rabbinic edict because of idolatry, and prostitution. If they have a fixed relationship than he is liable because of the Rabbinic edict of niddah, maidservant, idolatry and prostitution. If he is a cohen then even if they have a transient relationship then he gets lashes according to the Torah because of prostitution (Vayikra 21:7).

Shulchan Aruch (E.H. 16:2): Concerning someone who has sexual relations with a non‑Jew – if the zealots don’t punish him and he doesn’t get lashes from beis din – then his punishment of kares is stated clearly in the Bible Melachi (2:11-12)….Rema: And this sin has a loss that is not found in other sexual transgressions – the child who results from a relationship with a maidservant or non‑Jewish woman is not his child (Tur citing the Rambam). However if he publicly has sexual relations with a non‑Jew the halacha is that zealots can kill him as is stated in Choshen Mishpat (425). Thus this transgression is included in arayos (sexual transgressions) and one is required to suffer martyrdom rather than transgress it (Yoreh Deah 157).

The Rambam and Shulchan Aruch seem to be saying that fornication with a non‑Jew is only a rabbinic prohibiion. However the (Hilchos Issurei Bi'ah 12:6) of the Rambam raises questions about this. It states that while the prohibition against marriage or the punishment from zealots is only when the relationship is public – he doesn’t say whether the punishment of kares is only for a public act or also for a private act. A similar question occurs in regards to the Shulchan Aruch.

There are a number of poskim who say that fornication even in private would be punishable by kares (learned from tradition. These are found in commentary to E. H. (16:4) include the Avnei Miluim, Beis Shmuel, Derisha, Bach and Chasam Sofer (E.H. 1:93) [see below]. So even for a person who is not bothered by the clearly stated rabbinic prohibition – he should be concerned about kares.

In addition there are those who say that there is an explicit Torah prohibition(Vayikra 18:21).

Targum Yonason (Vayikra 18:21): And don’t give from your seed in sexual intercourse with a daughter of the nations that she beget a child that will pass over to idolatry…

Aruch (Aram): Megila (25a): Whoever says that Vayikra (18:21),”Do not give your seed to Moloch” means you are only prohibited from having sexual relations with an Aramean woman because then your child will be given over to the worship of the god Moloch – which implies that it is permissible with other non‑Jewish women – he is silenced and rebuked. Rather the explanation of the verse is as stated in the braissa cited by the gemora. The school of R’ Yishmael said that this verse is describing someone who has sexual relations with any non‑Jewish woman who gives birth to a [non-Jewish] child who will be for idolatery. That is because there is no difference between the idolatery of Moloch and other idolatry….

Chasam Sofer (E. H. 1:93): The Avnei Miluim wrote that even though a Jew who has relations with a non‑Jewish woman that there is a distinction between in private or in public [for the law of zealots killing them] , nevertheless when a non‑Jew has relations with a Jewish woman there is no such distinction. Futhermore in private there is also kares [when a Jew has sexual relations with a non‑Jewish woman. This is learned from Sanhedrin (82a), Rav was made to read in a dream that G‑d cuts off the man who does this [has relations with a non‑Jewish woman]. Since the view of the Rosh should be maintained the questions arises whether a cohen’s relations with a non‑Jewish woman invalidates his right to serve as a priest as ervah (Torah sexual transgressions) do? This seems to be refuted by the gemora in Yevamos (455a) which states that sexual relations with a non‑Jew or slave do not produce a child with the status of mamzer. That is because mamzer only results from sexual relations with someone classified as ervah or kares. It seems clear from this gemora that even though a Jew having relations with a non‑Jew is punished by death at the hand of zealots and he is liable to the punishment of kares learned from tradition – nevetheless this is not considered ervah. These are the words of the Avnei Milluim. I want to add support to his position. Megila (25a) says that anyone who interprets the verse “Don’t give your seed to pass over to Molech” to mean don’t impregnate a non‑Jewish woman – is silenced and rebuked. Rashi explains that the reason for this is that he is uprooting the true meaning of the verse and is saying incorrectly that one who has relations with a non‑Jewish is liable to kares and that the man is liable to bring a chatos if he does it unwittingly and he is executed by beis din if he does it deliberately after being warned. It can be concluded from this that even though a person is liable to kares for having relations with a non‑Jewish woman in private and can be killed by zealots if he does it openly – nevertheless this relationship is not considered ervah for which there would be execution by the beis din and also a chatos if he did it unwittingly. Thus this is consistent with the proof brought from Yevamos (45a). Consequently the cohen is not invalidated from his priestly duties by sexual relations with a non‑Jewess.

Maharsha (Megila 25a): R’ Yishmael – the verse describes a Jew who had relations with a non‑Jewish woman. According to Rashi it R’ Yishmael is cited in the gemora to describe the mistaken view that the Mishna says is to be silenced. And thus is supporting the view that the verse is referring to idolatery. However according to the Aruch [s.v. Aram] it appears that R’ Yishmael is cited as to the correct view of the verse. The Aruch asserts that the correct understanding of the verse is that it prohibits having sexual relations with a non‑Jew. The Aruch therefore says that the view that the Mishna wants silenced is the assertion that the prohibition of sexual relations applies only the Aramean women who are associated with the idolatry of Molech [when in fact it applies to all non‑Jews]. The view of the Aruch is also relevant according to the understanding of Tosfos Yom Tov…

Tosfos Yom Tov (Megila 4:9): A person who says Vayikra (18:21) prohibits sexual relations with a non‑Jew is silenced and rebuked … I have found in the Aruch (s.v. Aram) that he writes concerning Vayikra (18:21) that it means who ever gives of his seed to the well known people who give their seed to Molech for example the Arameans. That is because you are causing that your descendants be passed over to Molech. This implies that it is permitted concerning other nations who don’t give their children to Molech. Therefore he needs to be silenced and rebuked. Consequently the true explanation of Vayikra (18:21) is as is taught by the School of R’ Yishmael. It refers to a Jew who has sexual relations with a non‑Jewish woman who begets a child which will be given over to idolatry – because there is no difference between Molech and any other type of idolatry. These are the words of the Aruch. Rashi on the other hand says that the gemora cites the School of R’ Yishmael as explaining the view the Mishna says not to have. It would definitely seem that even according to the Aruch the citation of the School of R’ Yishmael is not coming to uproot the meaning of the verse and insist that it is saying the a person who has sexual relations with a non‑Jews is punished with cares… The understanding of the Aruch is supported by the Targum Yonason which says “Don’t give of your seed in sexual relations to a non‑Jewish woman who will beget a child for idolatry.”…