Halakhah su Deuteronomio 21:18

Although Rav Moshe did not prohibit smoking entirely, even he agrees that it is forbidden to smoke if one did not begin the habit before 1981.¹²Rav Moshe presumably would require one who began smoking after the time of his ruling to quit. He explains that it is forbidden to habituate oneself to and develop a desire for frivolous worldly pleasures. Rav Moshe also discusses this idea in another responsum (Teshuvot Igrot Moshe Y.D. 3:35), in which he rules that it is forbidden to smoke marijuana or use any other illegal drug. His source is the concept of the ben soreir u’moreh (see Devarim 21:18-21), a rebellious son who is punished for developing frivolous worldly desires (see Sanhedrin 68b).

[For a man] to not have intercourse with males: To not have intercourse with males, as it is stated (Leviticus 18:22), "And with a male you shall not lay, the layings of a woman." And Rambam, may his memory be blessed, wrote (Sefer HaMitzvot, Mitzvot Lo Taase 350), "And this negative commandment about this very matter is repeated in another place, as it is written (Deuteronomy 23:18), 'and there shall not be a kadesh from the Children of Israel.'" It appears that the rabbi, may his memory be blessed, does not agree with that which Onkelos translated (Onkelos on Deuteronomy 21:18), "and a man of the Children of Israel shall not marry a woman maidservant" - the understanding of which is a Canaanite (gentile) maidservant. Rather, his opinion is that " there shall not be a kadesh" only comes as additional negative commandments for male homosexuality, [just] as there are several [other] warnings (negative commandments) that are repeated with different words. And I have seen about Ramban, may his memory be blessed, (Ramban on Deuteronomy 21:18) that he also does not agree with the translation, but would say that the negative commandment of "there shall not be a kadesh" comes to warn that we not allow there to be among us - the holy nation - a kadesh; and that is a man who is designated to lay with men, as is known about them in the lands of the Yishmaelites to this day. And because of this, it is stated "from the Children of Israel" - since we are not warned from this with the [other] nations. As if there was a kadesh from the nations - and even amongst us - we are not warned about him; as we are not warned (commanded) about others besides us, except for idolatry alone.

And Ramban, may his memory be blessed, does not hold of this approach and he does not lean towards it; but [rather] he holds that there always be an explicit warning about the one to be lashed or about the one being killed - and not from a general negative commandment. And even if Scripture makes his death penalty explicit a hundred times, the Rabbi will still say that it does not punish unless it warns (and not from a general negative commandment). And he does not consider a general negative commandment as a warning in the place of lashes, because of that which is a famous law in our hands, "We do not administer lashes for a general negative commandment." And therefore he, may his memory be blessed, said that they already clarified in the Gemara from which verse we learned to administer lashes to the rebellious son: And they said in Sanhedrin 71b, "It is like Rabbi Abahu, as Rabbi Abahu said, 'We learned lashes for one who puts out a bad name, as it is written about him (Deuteronomy 22:18), "and they shall chasten him," from "and they chastised him" (Deuteronomy 21:18) that is written about the rebellious son; and "son" from "son" [in] "And if the evildoer be a son of (liable for) lashing" (Deuteronomy 25:2).'" And there is also a difficulty for Rambam, may his memory be blessed, in this, [since] he writes in the second root, that we do not give lashes by the power of a comparison (which is what seems to be indicated here). And he also challenged the Rabbi about his statement that the rebellious son is liable for the death penalty for his indulging in much eating and he did not distinguish between the first eating and the second. But they said explicitly in the Gemara in Sanhedrin 71 that we do not punish the first eating of the rebellious son with the death penalty, but rather lashes, as they said, "We warn him in front of two [witnesses] and we lash him in front of three. [If] he goes back and goes bad, he is judged by twenty-three [judges for the death penalty]." He, may his memory be blessed, also wrote and this is his language, "And what is fit to take out from this is that the first eating is prevented (forbidden) and its punishment is lashes, and the punishment of the second is death, and they are two preventions (negative commandments) in the tally of commandments, and they are [both] included in 'You shall not eat upon the blood.'" To here [are his words].