That’s because they don’t know how to deal with being labeled a homophobe.
I'm not the least bit afraid of homosexuals, but what they do disgusts me. If that makes me a "homophobe" than so be it. It's right up there with Al Sharpton labeling someone a "racist"...it carries no weight.
In those political forums in which I participate, I try to make it clear that I remain unimpressed by mere attitudinizing.. And that includes the use of any words that end with the suffix, "-phobe" (such as homophobe), as well as any words that end with the suffix, "-monger" (such as warmonger, hatemonger, or fearmonger.
Once others understand that one is simply not intimidated by their opprobrium, most will cease attempting it...