Lets see, reasons against gay marriage.
1- It's against my religion. (Fine, don't do it yourself then but you have no right to force your beliefs onto others.)
2- Marriage was created by religion. (Give me proof your religion or any other created/owns marriage, and explain life long mating pares of animals such as albatrosses. Religion makes use of existing social concept of marriage, it did not make it.)
3- Marriage is for procreation only. (Then sterile, old people, those who do not want kids and those who have stopped having kids can not get/be married.)
4- Hetro marriage is needed to continue the species. (As stupid as this one is, since it popped up I'll mention it. There are 6 billion of us and counting, AND homosexuals can have children, be it lesbian couple with in vetro/sperm downer, male gays at sperm banks/"helping" a couple conceive a child.)
5- But gays can't have kids so why would they want marriage anyway? (They can have kids, lesbians can give birth to kids, both men and woman can adopt children.)
6- We will all turn gay if we let them marry! (So do you secretly want to have anal sex with a big harry man? I thought not, and you are not alone so don't worry.)
7- They want to turn our children into homosexuals! (No they don't, as far as we know homosexuality is more genetic then physiological. If you raise your child to believe homosexuality is how they have to/should be regardless if they are gay or not, then it's your failure as a parent.)
8- They are all/mostly child molesters! (No, they are not. Many studies have been done, ranging from gathering of information form abuse cases to measuring the physical response of homosexuals, there is no link between the two.)
9- God punishes gays [eg, with HIV]so it must be wrong! (God got nothing to do with it. Stupid choices such as unprotected sex is the cause and you are no more immune to whatever effects them then they are.)
10- Gay marriage will destroy my marriage. (Once again, do you secretly want to have anal sex with a big harry man, and your wife secretly want to bed another woman? I thought not. If your relationship is so fragile that gay marriage will destroy it then you shouldn't have gotten married in the first place. You are married to someone you love and want to spend the rest of your life with, gay marriage, government and whatever else isn't going to change that.)
11- Gay marriage will make a mockery of my marriage. (I'm assuming you where married in a church, so already most of the worlds marriages make a mockery of yours because you do not agree with them or are unacceptable to you, gay marriage is no different. The real reason though is probably that you hate gays so much that you can not stand the thought that they get the same rights as you even if they have no impact on your life.)
12- They will make their children gay! (No, they won't. Studies have been done and no link has been found.)
13- Their children will turn out "wrong" somehow! (No, they won't. Studies have been done and on average children of gay couples do as well or better then children of heterosexual couples.)
14- Their children will be mercilessly picked on by other kids! (Aside from being a weak excuse, this is blaming the victim. It is the fault of the child & his/her parents that pick on the one with gay parents, and if allowed/encouraged then the fault of those in authority.)
15- It's not natural so it shouldn't be allowed! (Actually it is. Homosexuality has been widely observed in animals, both in the wild and captivity. This included life long breeding pairs. We are not some sort of alien life forum to this world that we share nothing with life on this planet.)
16- It will destroy our society. (No, it will not. Several countries have already allowed gay marriage so you can see the results for yourself. Those who are not gay will not change if gays marry, and gays will not fulfill their secret evil agenda that you believe they have once gay marriage is allowed.)
17- Ewwwwwwwwwwwwwwwwwwwww. (Stop picturing a big harry man anally raping you then. What they do is behind closed doors, you don't have to watch. But I do agree that no man should walk around in public in a speedo.)
So, am I missing any? If you disagree, please provide facts (quoting your holy book does not count unless you clearly back up what it says with facts, and no cherry picking facts while ignoring others that discredit what you say).
As for USA laws, not my country and not my problem.