In describing actions causing defects in children are Chazal describing medical facts or rabbinical curses?

I just came across and interesting article in 'Asia vol 73-74 pp 139-144 (  סכנתא או איסורא בהלכות תשמיש) by Rav Yehuda Hertzl Henkin regarding the nature of the statements of Chazal. We have discussed extensively the issue of causality ascribed by rabbis to events such as the Holocaust. There is a general obligation to try and search for the causes of misfortune in order to do teshuva and avoid wrong doing. There remains the question as to whether these causal descriptions of historical events are accurate or whether they are primarily motivational

Rav Henkin introduces a new dimension in this article. When Chazal say that if you do X then Y will happen - are they describing reality? What if the consequences they describe don't happen - does that mean that they were wrong or does it simply mean that nature has changed? Or perhaps all they mean  is that the consequences are more likely to happen if you do X but the change is only an increase in the likelihood - not that they will certainly happen.

The gemora being analyzed is Nedarim (20a-b) which is the basic text dealing with what is permitted in sexual relations.

Nedarim (20b): R Yochanon said, The above view [that talking, kissing or looking at her genitals or having unnatural sex produces defects in the children] is the view of Rabbi Yochanon ben Dehabai. However the Sages have said that the halacha is not in accord with his view but rather the halacha is that all that a man wishes to do with his wife he can do. This is comparable to meat which comes from the butcher. If he wants he can eat it salted, roasted, boiled or baked. And similarly regarding fish that comes from the fisherman. Ameimar asked, And who are the angels [that told him this]. They are rabbis. Because if in fact actual angels told him that the actions produced severe defects in children then why isn't the halacha in agreement with him? After all the angels are very knowledgeable about the nature of embryos! But why are these rabbis referred to as angels? Because they are as distinguished [by wearing white garments and tzitzis – Shabbos 25b] as angels.

Rav Henkin notes that some of the authorites dealing with appropriate behavior state that certain behavior is prohibited because of lack of modesty or the prohibition not to do disgusting things or even that one must love his fellow human being. Thus they clearly hold that these are either Torah or Rabbinic prohibitions. On the other hand there are a number of gemoras which say that inappropriate behavior causes severe defects in the child - such as epilepsy, blindness, deafness, mutism as well as spiritual defects such as an overwhelming yetzer harah.  These latter authorities are describing biological or medical dangers. The problem is how do we understand these statements when in fact to the best of our knowledge these behaviors don't produce the stated consequences? Is there an argument in medical reality?

 The gemora above notes the if these statements came from actual angels who really know what goes on - then they could be accepted. But since the source is a group of rabbis who apparently don't have special knowledge of the subject - Chazal reject their view.

If these "angels" don't have special knowledge then on what basis are they making their claims? Is it simply to scare people into behaving - even though they know the claims are not true? Perhaps it was the common understanding of the doctors of those times - even though they were mistaken.

Rav Henkin seems to suggest that the rabbis were well aware that they didn't have a medical basis for their claims. He suggests that these rabbis wanted to curse people who acted inappropriately and say that people deserved this to happen - not that it was going to happen. It seems that Chazal rejected this minority proposal and said that a person shouldn't do these things because of piety, modesty, respect of others or not to be disgusting.

והיה ראוי לפרש שר' יוחנן בן דהבאי איסורא קאמר ולא סכנתא, וחז"ל הם שאסרו לעשות מעשים אלה והם אמרו על דרך הקללה שראוי שייענשו על ידי הולדת בנים בעלי מומים. ולא שבאמת נולדים כן ושלא ככל הנ"ל. כלומר שאינו ענין טבעי כי אז מלאכי השרת בקיאים בטבע יותר ממנו, אלא הוא עניין גזירת ואיסור חכמים. וניחא שלא נחלקו במציאות שר"י בן דהבאי סובר שדברים אלה גורמים למומים ורבי יוחנן סובר שאינם גורמים למומים.

Would appreciate anybody letting me know if they have seen a similar explanation