This site actually points out both the good and the bad on Same sex Marriages. It’s really quite interesting if you take the time to read it, which I suggest you do.
Denying them is a violation of religious freedom (civil and religious marriages are two separate institutions).
Marriage benefits (such as joint ownership, medical decision-making capacity) should be available to all couples.
It doesn’t hurt society or anyone in particular.
The only thing that should matter in marriage is love.
The number of child adoptions should increase since gay couples cannot pro-create (although some might see an increase in gay adoptions as an argument against same-sex marriages).