In the broadest scope I've never understood why there has to be laws concerning marriage
Because it is one of the very few institutions found in all human cultures. Any legal system that doesn't deal with marriage in some fashion is profoundly deficient. I'd prefer that we separate the legal and spiritual aspects, but that's a separate argument.
The use of judicial fiat just creates anger and inhibits the building of consensus. It isn't something WE did, it's something THEY forced on us.
This, this, a thousand times this. Telling people "fuck you, that's the way it is, and no you have no choice" is why the US still has a huge anti-abortion lobby.
violent crime keeps decreasing but our prison populations keep rising
Some would say that the latter is a direct cause of the former, in which case it needs no further explanation. You just put the Bad Guys in prison, on whatever charges you can make stick (even if non-violent), and violent crime goes down.
Life is a healthy respect for mother nature laced with greed.