You are correct, but in addition, it is discriminatory for the state to pick which sexual deviancies it wishes to promote and “protect”, and which it does not.
Compare polygamy and homosexuality, for example. There is more agitation for sanctioning same-sex “marriage” than for sanctioning polygamous marriage. Why? Well, for no other reason than that the homosexual lobby is powerful, well financed, and fashionable.
If human-animal sex became “chic” tomorrow, we’d start seeing people demanding anti-discrimination laws against people who are sexually attracted to sheep.
But as of now, out of all the various perversions and sexual variations that exist, ONLY homosexuality gets promoted in this way. There will be no leather fetish night at a Padres game. Only a gay night.
I don't see how this is "promoting" behavior. Lots of married people engage in deviant sexual behavior. The fact that these folks aren't denied housing doesn't mean the government is promoting oral sex. Does government promote Hinduism by banning discrimination against Hindus?
Equal protection under the law, no more but no less.