I am not really against "gay marriages", gay people have the same right to form a couple and be recognised as everyone else. Whether religion agrees with that shouldn't matter, because religious principles are not the law. I don't really like the idea of calling "marriage", but that's a minor issue. However, I am worried about what civil union would bring along. Like Ghis said, in France they have PACS, in Spain we have "parejas de hecho" (in some parts of the country), which are the equivalent to marriages, but easier to break and IMO they demand a lot less commitment. I am afraid some sort of gay union would be applicable to heterosexual couples, who can already celebrate traditional marriages, giving them the opportunity to receive the benefits of a marriage without suffering the consequences. That's my only issue against it, I'm not even sure it'd happen like that in the US, but it's part of my dilemma about making those unions legal.
(does this make any sense to anyone? I'm just not sure I explained myself right lol)