You know, it's really quite simple. When a government has a legitimate interest in preventing marriages (marriage between blood relatives, for example), it can, and should, do so. When there is no legimate reason to prevent marriages between certain types of people (inter racial marriage, marriage between gays), then the government cannot prevent such marriages.
There is no legitimate reason whatsover for preventing gay marriage. Intolerance and bigotry are not legitimate reasons. I have yet to hear a valid, logical argument against gay marriage - they are either red herrings or bull shit arguments designed to mask the true reason for the opposition: intolerance and bigotry.
How is it IN THE GOVERNMENTS interest to stop blood relatives from marrying?
I thought the criteria was that they love each other, be consenting adults and all was right with the world.
Be warned if you are going to claim defects first generation defects from blood relatives is so minor as to occurrence as to be irrelevant, further the Government allows people that have a 50 percent chance to pass on a defect to marry and breed.
Other then your ick factor why should blood relatives be prevented from marrying?
Well, it is not technically true that blood relatives cannot marry. Beyond certain degrees of consanguinity, blood relatives are allowed to marry. I haven't reviewed this in some time, but I think that second cousins and beyond can marry.
You are joking when you ask why blood relatives are not allowed to marry, right? In case you are not - if blood siblings (brother and sister) produce a child, genetic defects can occur. If marriages between blood relatives continue in that same blood line, things can get really messy.
Remember the little guy with the banjo, sitting on the bridge as Burt Reynolds and his pals embarked on their little canoe trip into hell in "Deliverance"? That kind of stuff.