The main basis of the argument is whether marriage=love or marriage=procreation. The main argument against gay marriage is the marriage=procreation group.
If the people against it TRULY believe marriage is only for the purpose of procreation, then shouldn't they be willing to all join a computer group where they all input their information and proceed to marry whoever the computer decides will match their belief in upbringing? So that there's no conflict whatsoever in their views on how children should be brought up? Because after all, marriage isn't about love.
Or should the computer base it entirely on genetics? These people who proclaim that marriage equals procreation should happily walk down the altar with a total stranger who is genetically most likely to create healthy children, or the smartest children, or the prettiest children with them.
Perhaps they will argue that they are (most of them) Christians (which I am one, by the way) and therefore God will lead them to the person who they should bear children with by the process of having them fall in love and that it's His wish that they should bear children with the person he deems them to fall in love with?
Well then what about the gays who consider themselves Christian? I'm pretty sure I remember that Episcopalians allow homosexuals in their church. Then, wouldn't God be saying whoever THEY fall in love with they should marry? Or should they, after banning gay marriage, go on to ban and discredit marriage in every religion that allows gays? Because after all, it can't be a true religion if gays fall in love while following that religion, right?
And they should probably outlaw divorce as well, because if God decides who you fall in love with, then he WANTS everyone to stay in miserable unhappy screaming-match marriages, for the children's sake. After all, marriage is procreation, not love.
Or maybe, juuuust maybe, these people who loudly proclaim marriage=procreation just disapprove of gays in general and are being selfish about who should be "allowed" to be married by restricting the rights of the underdog.