TL;DR much Darvan?
The gay marriage thing is more a matter of equality. There was no logical reason to deny same-sex couples marriage. Of course marriage is, in my opinion, a hassle and not worth the benefits it may provide (I am actually ignorant to the perks of being married, sue me). You don't need to marry someone in order to love them and live your life with them (at least in modern countries like the US).
This whole gay marriage issue is very much like the issue of topless women we had in Canada a while back. To summarize, men could be topless in public but it was indecent exposure if women were topless in public, so women protested for that freedom and they got it. Of course, one of the biggest reasons they fought for this was gender equality. After the protests there hasn't been a single topless woman that I've seen in public.
It's all a matter of principle.