I have seen no society collapse for treating LGB people equal, but there is plenty of evidence that homophobia actually causes harm.
Well, in all fairness how long have LGBT-tolerant societies been the status quo? I'm counting about 45 years in the U.S., which is a drop in the bucket in the optic of historical trends. It remains to be seen how these new laws & freedoms affect the mores and fabric of the general population in societies where they're enabled; particularly this is true for same-gender parents and how their children will develop as a result (far too novel yet to judge).
What is certain is that if the majority of the world population was uniquely attracted to same-gender partners, the population would decline through attrition until finally only baseline levels of existence would remain. There's therefore an evolutionary case for being straight or bisexual that is missing for a purely homosexual person. To be fair, there's millions of able-bodied, hetero men who can't procreate because they can't find a partner. There's also straight couples that can't bear children without surgical procedures or surrogates. But their numbers in the population are relatively marginal so that the trend towards population growth continues more or less in linear fashion. That would not be true if the opposite was the norm.
Somewhat tangential but you have to wonder why it takes endless infomercials, rallies, talking heads on TV newsmagazines, celebrity spokespeople, entertainers and anti "hate" laws in order to get 'equality' on the same playing field for gays as straights. Force-feeding it by fiat and through mass-media manipulation of gullible (white) under 35s has an artificial quality to it that suggests it's not through the will of the people but rather through the machinations of a small special interest lobby & their powerful friends in the legislature that these 'improvements' in social standing through egalitarian lawmaking actually materialized. It feels as fake as the enthusiasm on display at 'Pride' events. The other side of the coin is that if one doesn't submit to or agree with this new paradigmatic trend towards unconditional acceptance, one is at once vilified by their coworkers, neighbors, local worthies, etc. What're they afraid of?