I'm still waiting to hear the explanation for why this is going to cause the downfall of civilization.
I'll attempt (probably in vain) to make this short. As a note before I start, I am strongly in favor of Civil Unions and reluctantly against gay Marriage for reasons specified below.
It won't particularly be the ultimate cause for the downfall of civilization but it will most certainly play a large role in the dcay of moral America. I ask everyone to look back to the 1950s when people started really noticing that some people are homosexual. It was extremely frowned upon and very taboo to discuss it. Now, fast forward to the 1970s and it still remains a taboo subject but is generally accepted as existing within America. Now, if you look at the 1990s, homosexuality was becoming a generic part of America but the thought of homosexual
couples was still somewhat taboo as were couples of more than two people. Couples of more than two people were becoming increasingly common by the 1990s as well but is well behind homosexuality in becoming a widespread "concept".
Now, the idea of homosexuality has been around for much longer than the idea of polygamy and has therefor been able to work its way into American life sooner than polygamy. If homosexual couples are granted the right to be married, then the moral line defining marriage has been erased and redrawn for a certain group of people. Those people having the line redrawn for them, expect other moral lines to also be redrawn, thereby growing the amount of things socially accepted and known to be morally "right". Once one group has the lines redrawn, the more other groups expect the same equal treatment, also claiming "Civil Rights" have something to do with it. The more groups that have that line redrawn for them in several different directions, the more broad America's morals become and the less defined they become, thus rendering them a thing of the past. The more expanded the line of accepted concepts becomes, the harder it is to refuse more expansions to other groups in other situations.
The more groups that force the moral lines to encompass them, the less the word "morals" means. If we accept gay marriage and polygamy, the more unfair to other groups it will become to deny them a redrawing of moral lines. Back to the 1970s, people were fighting for the right for homosexuals not to be frowned upon by societies morals and never imagined they would get any further than that. The further people get with pushing the lines of morals, the more they want to go even further.