That's like saying laws against gay marriage aren't discriminatory because straight men aren't allowed to marry other men either, so everyone's being treated the same. It's 'true,' but it's disingenuously true. "Hey guys, you can have all the sex you want, just make sure it's only penises going in vaginas!" HMM WONDER WHAT THAT SOUNDS LIKE. I'm not the foremost authority on gay sex, but I'm at least in the top 10, and there's generally no penis-in-vagina action going on.
I also find the childfucking priest example to be disingenuous. The law as it currently stands allows a (male) teacher to do the same thing with an underage (female) student, and yet no one seems to be upset about this despite heterosexual men far outnumbering non-heterosexual men and the latter example consequently being far more likely than the former. Either the state of California is currently using the (existing) law to allow all sorts of abhorrent degeneracy (possible, I haven't checked, but no one seems to be complaining about that so I find it unlikely), or there's no reason to assume the priest wouldn't immediately be deemed a sex offender by the judge, and gay people being involved is the only reason people are getting upset about this, because... well, I don't really need to say why, do I?