This has been a long running mystery to me.

Can somebody explain the issue with gay marriages in USA? I know it's an issue over there, I just can't figure out what it's based on. I was trying to think of a good hypothetical argument against it, but failed. The people who are against gay marriages, what are their arguments? I'd like to know how opponents to gay marriage reason? I'd have thought that the freedom of religion and freedom of expression, which arguably is the ultimate religion of USA, would have that covered.

I did a quick search, and all I found was pretty confusing and incoherent. I need to have this explained in detail. There must be more to it than this. Because all those arguments are basically being against it out of spite. So there must be a deeper political reason that's hard to see just looking at the issue as such.

Please enlighten a poor dumb Swede.