Rav Kook supports Argentine rabbis' measures against insincere conversions

Rav Kook(Daas Cohen Y.D. #154): [Written to the rabbis of Argentina] Even though the halacha is that those who convert for ulterior motives are valid gerim (Yevamos 24b) and this includes a man who converts for the sake of a woman and a woman who converts for the sake of a man, it appears from Tosfos (Chullin 3b) and Yevamos (24b) that this is only if the conversion involves a full commitment to keeping the mitzvos. But if the conversion is not complete –meaning without full observance of the mitzvos and also the motivation was not proper – then they are worse then regular lion‑converts that are mentioned there in a braissa. There is one opinion that these lion‑converts are genuine gerim but they are like the Kusim because according to the view that they are lion‑converts they are considered according to the halacha as total non‑Jews because there are two problems. 1) the conversion was not for the sake of Heaven 2) they don’t fully observe the mitzvos because as a minimum they worship idols through shituf as is learned from the verse “and yet they still worship their gods.” The language of Tosfos in Chullin is that they didn’t convert completely and thus it was not only idolatry that they violated. Thus in any case where the mitzvos are not observed properly and the motivation wasn’t proper – then there is no conversion at all. We see this in the language of the Rambam and Shulchan Aruch (Y.D. 248) that a person who converts for ulterior motivation, we are concerned about him until his righteousness is established. In other words if we see that he is not conducting himself properly according to the halacha and he had ulterior motivation for conversion – this is not considered complete conversion. In fact by accepting a ger who is not going to be observant, we transgress the prohibition of placing a stumbling block before the blind in any case. For if we say that the conversion is not valid even bedieved and yet we accepted them – then that causes problems for society because they are treating non‑Jews as Jews. How many snares and destructions results from that – especially concerning kiddushin, gittin and yibum. The Jewish husband will mistakenly view their son as his son and if he has a Jewish wife afterwards and he dies without other children, his wife will be mistakenly allowed to remarry without chalitza even if he has a brother. There are many other harmful cases that can result. On the other hand if they are truly gerim then bedieved they are fully obligated to keep the entire Torah. Then the beis din causes the gerim problems because they are now obligated in punishment because of all the Torah prohibitions they are violating. Prior to conversion they were not obligated and not punished for transgressing the Torah. We see this in Yevamos (47a) that we are to instruct the candidate for conversion the punishment for not keeping the mitzvos. We tell him , “you should know that before you came to convert, if you ate chelev fat there was no punishment of kares. If you transgressed Shabbos you would not be punished with stoning. However once you convert , eating chelev fat is punishable with kares and profaning Shabbos is punished with stoning. Thus we see that we are commanded about lifnei ivair (placing a stumbling block before the blind – even for non‑Jews. This is stated in Avoda Zara (6b): How do you know that you should not offer a limb from a living animal to a non‑Jew? Because the Torah says “do not place a stumbling block before the blind.” And it is a kal v’chomer concerning our case because he causes him to be have a great obligation as a Jew and he will be punished for his transgressions of the Torah. Therefore it is wonderful what you and the other holy rabbis [of Argentina] have done in making and strengthening the boundaries in Argentina where there is a great breakdown in the walls and there is a great number of gerim who are not sincere – and you have decided not to accept gerim at all. Whoever genuinely wants to attach themselves to the holy Jewish people should come to Israel where they will carefully be evaluated by the Jewish courts. Only those who are genuinely committed to converting for the sake of Heaven and will be fully observant - will be accepted…