Why is endorsing gay marriage/civil unions bad?

[MissBrattified]

Personally, I have two main thoughts on this issue, and they are surprisingly liberal:

1. I wish churches had jurisdiction over marriage ceremonies. Religious ceremonies should be held for those who want them, and everyone else can form secular (civil) unions. Giving this power back to the church and having the state only take care of paperwork and names and dates is the way it should be, IMO.
2. I don't really care WHO wants to form a civil union--whether its for the sake of sharing a household, sharing incomes, sharing dependents or sharing a bed--I really don't care. That's a legal issue that has nothing at all to do with the sanctity of God-ordained marriage between a man and a woman. IMO, if roommates want to file a civil union for the 4-8 years they attend college so they can share household expenses, etc., they should be able to do so. It's a practical matter.

When I was about 13, we lived next door to a monogamous gay couple. One of them worked at the hospital as a nurse, the other one was a businessman. They had two very fat, spoiled, sweet basset hounds. I don't remember my parents ever being rude to them or complaining about them living next door. I certainly was never bothered by them, and I find it interesting that my parents didn't seem particularly bothered by them either.

My point is: I don't see the point of Christians digging in their heels and trying to prevent people from sharing bank accounts and filing joint income tax returns.