It's about feeling the need to give pleasure to the asshole. I don't care if you're gay. That's fine. I care if the people you want to please are murderous authoritarian dictators. If you think that's homophobic, then that's implying you think being gay makes you love dictators, which would be an odd belief to hold.
If you want to suck a morally upstanding person's cock, that's a good thing.
If you want to suck an evil person's cock, that's a bad thing.
It isn't the cocksucking that's at issue.