Ubiq, you’re reducing morality to relativism.
Let’s break this down: causing harm to others is something that was and is accepted as bad by the world and by the Torah. The motions of (insert italics) what causes that harm (end italics) will be based on our best knowledge, and can be mistaken. It can also be relative to the times, because something considered hurtful 100 years ago today might be considered by the people who are being affected as harmless. Those are fluid; almost everyone referred to black people as “negros” in the 19th century, not in a pejorative. Today that is offensive.
What is not flexible, is the morality of the issue itself. It was and always is immoral to cause someone harm. Whether or not abuse always caused this level of harm, or whether or not people were aware of that reality (or your case of smoking) does not impact the value under discussion, namely harming others.
Homosexuality, however, is a moral issue in itself. It’s a specific sin, but it is under a larger category of perversions that are included in the 7 mitzvos bnei noach, as they are intended to be appreciated logically for their evil.
Rav Moshe is saying that goyim typically understand this; it’s part of our moral compass. The fact that we live in a depraved time when people don’t understand that doesn’t change our approach ideologically to the sin. What the Torah calls a perversion or abomination remains such. That means we are to be disgusted by it for all times. It’s not relative any less than the halacha its attached to is.
Lemosh, according to your view, if we live in a society where murder is acceptable when it’s, let’s say, in a duel, are we to say that while it can’t change the halacha that states that one may not kill another, we need to adapt our intellectual approach to murder in light of the society we live in? Are we to say that murder is any less evil in that society, but alas, we are anusin mipnei hadin and must maintain our policy of not murdering?