My question is, the people who are opposed to gay couples having the same rights as their straight counterparts... why do they want to deny the rights of an entire group of people??
I suspect that the reason is not direct. It is rather a mix of more nebulous drives- that of affirming/validating self and fear of the other (leading to mob mentality).
It would be I think fairly safe to assume that every person against gay marriage, or let's say granting equal rights to gay people would be those who do not identify with being gay (and that in itself is complex enough.) If I took the liberty of saying that every action is derived as the result of two primary emotions love and fear (for the sake of simplicity only) then one could say it was derived from a love of self, and a fear of non-self. By this, I mean that a person who is attached to their sense of identity will want to preserve this by validating themselves, and therefore perhaps raising it in worth relative to other people. If sexual orientation is an important factor (and sadly it has been for yonks), then one will wish to assert their sexual orientation as being acceptable and superior over the others. This practice is rooted in the prevalance of normative claims and their moral implications.
Wishing to deny an entire "group" of people a right therefore might be masked in "defending a right cause" like some crusade. These people somehow derive a sense of self-worth from what they are doing as it not only gives them a sense of superiority, but a scapegoat to project the inferiority of otherness that their self-worth entails. It's of course easy to do this when you have numbers on your side.
In short, people like to think that their actions are a result of their beliefs, which are somehow justified because they are grounded in some concrete determinant of value. To me, much of the earlier debate is very relevant on a social level- because as you all know most forms of major Western government were originally tied to religion, but I'm under the impression our political ideals hold that politics should be kept separate from religion (not least because cultural boundaries in democratic states are no longer as concrete as they used to be). However, decisions on leaving it to the church etc. really to me resemble social niceties (an explanation as to why would have me post long essays on Christian doctrine which isn't so relevant to this thread), because an essential distinction must be made between how we handle practice of beliefs, and what moral judgments can be made on the matter.
What posts like Sarah's highlight is the irrationalistic absurdity that arises from simple drives and the inability to discern the trees from the woods. This means that a denial of rights here constitutes either blatant ignorance, or hypocrisy.