Homophobia is a relatively new concept and has really only popped up in the last few years. To expect the entire population of the world to change their views in order to respect a sexual orientation does not happen overnight, it takes generations and decades. You need to change people's mindsets and unfortunately it's not through the use of leaving a roleplay if you are not happy with someone—who you don't know—saying a few phrases that you are concerned about.
To give an example, I say fag and gay in my daily language, my manager at work says words like that, and we've had conversations with slurs and slang using an assortment of swear words. Not let me point out... My manager is a homosexual. 100% gay and even has the little quirks and giggles sometimes that show that he's got a real feminine persona, but he still uses a variety of "gay" associated words in his normal speech. (we are Australian btw, so swearing is almost like a passage of rite)
Personally, I wouldn't be ditching a roleplay so quickly because you have a hunch that someone may be a homophobe. You don't know them—just as they probably don't know you—and all you are doing instead is judging them before you have had a chance to know who they are. People are not one dimensional generalisations, they have multiple positives and negatives, a lifetime of experiences and being raised in a certain tradition by a certain family of whatever background. If you get to know them a bit more and they're still an ass, that's fine... But I would get to know them a bit more first.
Ideas die hard.
If they where easy to kill off we would have no Nazi, confederates, or others still running about and still dangerous. Even up to a Century or longer after Thete defeat.