Faggots are offended by the epithets used against them because they know, deep down, that they are degenerate scum. If they truly believed that their lifestyle was not wrong at some deep level, merely calling them a name that points out their lifestyle would not be offensive at all. This is why their attempted epithets against straight people fail. Straight people are not degenerate (at least not on account of their preference of sexual partner), so any attempt to deride them on that basis will be unsuccessful.