I've had debates with the brazenly homophobic and those who are simply ill informed, under educated or just towing the line quite often, but in all reality, I have very little interest in changing their minds; much of the time, the intention behind the debate is "collateral damage," if you'll excuse the politicking vernacular; it's those on the sidelines listening in who will hear one side using perjoratives, distortions, exaggerations, pervasive misconceptions, quote mines, misrepresentations and the other simply exposing the prejudice for what it actually is.
Those who are brazenly homophobic, more often than not, are too in love with the easy self definition their particular tribal enemy of choice provides. In that regard, you are not looking to change their opinions per se; you are challenging their sense of self, which is why it is so incredibly difficult. I would like to think that I leave them with something to think about: one of my tried and tested tactics that NEVER fails is to allow them every presumptions and misconception they like to assert, then ask: "So what?" For example, one of the things you will often get from certain kinds of homophobe is the assertion that homosexuality is a "lifestyle choice," (emphasis on CHOICE).
My response: "So what? For the sake of argument, let's allow that; let us assume that the proclivity to be attracted to members of the same sex is a matter of conscious choice: how does that legitimise your prejudice and hostility?"
You'll find them floundering, not really knowing what to do or say most of the time, as they haven't actually thought about it very deeply, and were expecting you to simply deny their initial assertion.
"Homosexuality is unnatural!!"
"So what? Watching T.V. is unnatural. Driving cars is unnatural AND, I might add, by any rational definition of morality, a much shakier choice, since statistically you are much more likely to cause harm or injury to yourself or others than anyone engaging in homosexual activity."
I'm more interested in exposing commonly parroted bullshit for what it is than changing the minds of those who use it, as the very fact that they DO use it is more than sufficient evidence that they have little in the way of minds to change.