Quite an amusing thread when read from a back seat. Sometimes I still cant believe some peoples views in this modern tollerant world. But you are trying to argue from points of view created by firmly held beliefs that will not be swayed by arguments from the other side logical or not.
2 guys i work with, one a member of a branch of the church of later day saints who believes being gay is not a natural occurance (no biological reason, although there is proof for this as im sure u could find the opposite
), and the other, a british muslim who truly believes that there are no gay muslim men because it doesnt "affect" them.
As for the marriage problem, for a church wedding, thats up to the church. It can keep whatever rules it wants, it doesnt have to "keep up with the times" or change its beliefs or whatever, the catholic church still bans the use of condoms. But civil weddings are different and should be allowed as it is a persons right to be married to whomever they wish as long as it does not harm another person / infinge on their rights etc.
Now for the privisos. Incestuous unions should not be allowed due to the genetic problems involved. Im not sure how accurately I have been informed on this but the reason you are not allowed to marry your brother sister aunt uncle etc up to your cousin, is that the genetic code is too similar and can greatly increase the risk of malformed children. Polygamist relationships are actually allowed in some religions. So just because you believe in one religion and have been brought up another way, does that give you the right to enforce your views on others?
On a side note, marrige is not an exclusively christian word. You can marry too parts together when making something as in they are "married together":
http://www.yourdictionary.com/ahd/m/m0121200.html
So you should not have a problem with a gay couple being allowed to marry.
EDIT: Ooops missed paedophiles. But i am sure that any sane person is not going to try and argue that the physical and emotional scars left on children through paedophilia is not harming them or infringing on their rights?