Much of the "biblical documentation" for agendas like homophobic hate campaigns come from the Old Testament. The best refutation of this IMO is demonstrate how the pushers of this agenda have quoted selectively while ignoring inconvenient texts that might undermine their credibility.
The classic on this, floating around the web since 2000, is the "Open Letter to Dr. Laura." It combines documentary evidence with ridicule done in a way that I admire very much. It is not shrill, it is quietly devastating.
Most of the versions of the Open Letter floating around lack the author's name and have added a few extra quotes. Here is a version that HAS the original author's name and also provides two biblical translations for each cited verse (at the end, after the list of quotes). I'll quote a sample of some of the quotes below. I suggest you read the whole thing and keep it with you to refute wingnut hatemongers
http://www-users.cs.york.ac.uk/~susan/joke/laura.htm(snip)
An open letter to Dr. Laura
J. Kent Ashcraft
May 2000
Dear Dr. Laura,
Thank you for doing so much to educate people regarding God's Law. I have learned a great deal from your show, and I try to share that knowledge with as many people as I can. When someone tries to defend the homosexual lifestyle, for example, I simply remind him that Leviticus 18:22 clearly states it to be an abomination. End of debate.
I do need some advice from you, however, regarding some of the specific laws and how to best follow them.
a) When I burn a bull on the altar as a sacrifice, I know it creates a pleasing odor for the Lord (Lev 1:9). The problem is my neighbors. They claim the odor is not pleasing to them. Should I smite them?
b) I would like to sell my daughter into slavery, as sanctioned in Exodus 21:7. In this day and age, what do you think would be a fair price for her?
c) I know that I am allowed no contact with a woman while she is in her period of menstrual uncleanliness (Lev 15:19-24). The problem is, how do I tell? I have tried asking, but most women take offense.
d) Lev. 25:44 states that I may indeed possess slaves, both male and female, provided they are purchased from neighboring nations. A friend of mine claims that this applies to Mexicans, but not Canadians. Can you clarify? Why can't I own Canadians? (snip)
I do recommend you read and savor all of it and keep a copy handy.