First off, your statement is false. There are quite literally millions of people globally who both support gay rights and do not think promiscuity is good. You might be confusing “finding promiscuity bad” with “condemning promiscuity”, which are obviously two distinct concepts. Even if they were considered the same, it’s still obviously not true.
Second, it’s clear that—generally speaking—developed western societies no longer “regard homosexuality as dangerous to harmonious society”. Otherwise there would obviously not be widespread support for same-sex marriage. That feeling isn’t universal yet, but it’s unlikely to be terribly long until society generally stops worrying about it.
Why should they even consider it? Their opponents usually dishonestly represent homosexuality as one of the worst forms of promiscuity (by the volume of their concerns, worse than nymphomania, cheating, pedophilia, fetish addiction, polygamy, etc.).
The answer to promiscuity is 1. Non of your business, 2. education.
Do you have many gay friends?
How about you take a look at any of the studies that have debunked it?
More to the point, a homosexual that adheres to traditional family values (ie: one partner for life, moderate sobriety, responsible adult) is much more appealing than one that exists outside of traditional family values (ie: promiscuous, heavy drug and alcohol use, other irresponsible behavior). In this instance (and numerous others), the basis of opposition to homosexuality is that acceptance invites degeneracy and destruction of harmonious society.
Do you think a majority of Americans have not had premarital sex?
The average American has 7.2 sexual partners over their lifetime. [1]
1. https://www.refinery29.com/2017/08/169555/average-numbers-se...
> Homosexuality and promiscuity are closely intertwined, my argument is that they must be disentangled for homosexuality to be generally acceptable.
So why don't you quit entangling them? The only reason homosexuality and sex positivity are entangled is because of the thousands of years of murdering homosexuals, oppression of women, oppression of polyamorous, etc.. the thing they have in common seems to be a series of hateful bedroom laws enacted by a wannabe theocracy.