This is both trivializing and infantilizing. The central premise of geneticism is that these things are wrong, and the only reason we shouldn't discriminate against these people is because they can't help but be wrong.
The argument then becomes that we shouldn't discriminate against people for something they can't change - the chief implication that, if it could be changed, it should.
That whole line of argumentation is horseshit and concedes the most important point of all to the fundamentalists: that one's sexual orientation or gender identity can be morally reprehensible.
What? The central premise of geneticism is that genetics underpins the majority of human attributes and behavior. (Note: I do not personally believe this.)
Notice that arguments that homosexuality is genetic is preceded by arguments that homosexuality is a choice. Instead of defeating the thoroughly shitty notion that homosexuality is inherently wrong, the argument is instead steered towards "yeah, but they can't help it".
Without the choice angle, geneticism would just be a footnote. Whether or not orientation and gender identity are genetic is entirely irrelevant to the morality debate, and its presence in the debate predicates upon the assumption that, if it weren't genetic, the morality of the situation changes.
This stretches beyond the sexuality debate, of course. Whenever the argument is made that we shouldn't discriminate based on things people can't change, the implicit baggage argument is that if we could change those things, we should.
The correct rebuttal is "there's nothing wrong with being gay/bi/black/yellow/red" not "but they didn't choose to be gay/bi/black/yellow/red".
Then I deny the existence of 'geneticism' as you apparently define it, and say it's a strawman argument against the notion that anything is determined or influenced by genetics.