1. Well we certainly don't need more survival at this point, we're already overpopulating. Humanity isn't dying out any time soon, especially since average life expectancy has been rising. The only reason we'd push strictly survival based procreation is when we're trying to raise the population of an endangered species, even then forced sex isn't Conservation International's main forteit. xD
2. I mean, I'm hoping nobody here condones forced marriages between legal adults and minors. But again, we don't really need survival, and it's not like banning homosexual marriages is just going to magically stop gay people from existing. Homosexuals already can't procreate, so the worst thing that will happen with legalization is perhaps some closeted homosexuals in relationships will leave, but that's incredibly minor compared to all of our other population problems. xD
3. I mean, I still have family inheritance things. It's not like by not having a father I just become exempt from everything. I mean sure it sounds a lot cooler to say, "5 generations of men built upon this tree fort," than to say, "4 generations and one homosexual built upon this tree fort," but really that's unimportant. My mom still gave me her old stuffed animals (they weren't that good though), my uncle gave me my first box of Lego from when he was a child and boxes of G.I. Joe figures (my parents gave them back recently though RIP in Pieces), and I'm still getting that special sense. I suppose you could use the argument for seperately gendered children (i.e. boy of lesbian couple, girl of gay couple) that there leaves a gap in proper role models, and from experience...I suppose it's kinda true. But it doesn't matter now does it? It just leaves a gap that the child themself can fill in. Now you aren't obligated to choose your father as a role model (who could also be a drunken mess but that's off topic), you could decide to look up to whomever (as long as they fit the basis of what your parents layed out for in morals, i.e. my hero isn't gonna be Adolf Hitler). So I don't really mind the missing role model of my gender, in some aspects it's even better than having a father (most would disagree though).