Marriage has been between only men and women only since the dawn of cilivilization, and for good reason.
Some men are attracted to underage boys. We don't let them marry.
Some men are attraced to underage girls. We don't let them marry.
Some people are attracted to more than one person. We only allow them to marry one person.
Attraction is not a license to marry.
The fact is that homosexuality has existed as long as (and probably longer) than organized, religious, marriage. I am not trying to equate a civil union with marriage in a church. What additional civil rights or civil benefits are conveyed upon someone who is married in a church? None. The benefits of a religious marriage are confined, properly I believe, within the applicable religion. Marriage has been a religious ceremony since the dawn of religion, so should we strike down all civil marriages between heterosexual men and women because they dilute the "original meaning" of marriage?
I am talking specifically about the civil benefits conferred upon the union, such as presumed inheritance, the right to make medical decisions for your loved one, the tax benefits, etc. And what would come with this, for those who take it lightly, would be divorce, alimony, child support, etc that right now, these individuals don't have to worry about.
As for the other scenarios you posted, I don't really think those need addressing, they are flame bait, and are off the point anyway. (in my opinion) Thank you for the opportunity to express my views in a cordial discourse.