I gather fundamentalist Christians are against gay couples because that is what their religious texts say, which let us face it are important to them because of their belief in God. They see homosexual behaviour is a sin laid out by God.
A sin that could land the person in strife. As for the type that are happy that gay couples divorce, well there could be a number of reasons one being the reduction of "sin" and one being smugness, again people can be smug on many issues, I find the attitude of The Westborough Baptist church cultic and repulsive, as I understand from the Bible Jesus hung out with the tax collectors and thieves because they knew they were no better than anyone else, they didn't self righteously believe that they automatically got a golden ticket to heaven.
Religion aside, I do know people who do not believe homosexual couples should bring up children because they believe children should have a mother and father role model. Psychologically says that not all homosexuals are born that way that some miss out on vital stages of development from lacking a sufficent role modelling from parents leaving the child facing their own gender, then some are sexually abused and so it becomes their normal. Of course none of this changes the internal struggle of the individual but it is a far more complex topic matter than a religious taboo, some just find the idea icky.
There are issues many topics raise that are not simply synonymous to religion. I know people who do not like Muslim temples being built in what they refer to as a Christian Country, ie England, and they are not Christian themselves. Religion then becomes chess pieces to hide behind.