Always with the slippery-slope argument.
Lol, "slippery slope." That ain't the get-out-of-jail-free card that you think it is.
Slippery slope is a fallacy when you assert that a change will lead to a completely unrelated change. Reducing the tax on gasoline will lead to more teenagers smoking dope, for example. There is no connection between the two, so one won't lead to the other.
It is also a fallacy when it ignores the principles at play. Take, for example, an assertion that someday the NRA will be fighting to allow kids to carry concealed guns in school. The thinking is that concealed carry for adults everywhere leads to concealed carry for children anywhere. But the principle in play is that mature, reasonable adults should have the ability to defend themselves with the best tool for the job. Children are not adults, they are not mature, so the NRA doesn't want them carrying concealed weapons.
Slippery slope does not apply when you are pointing out the logical extension of the principles at play. Let's say that a group organizes tomorrow with the name of Mothers Against Fast Cars. This group believes that speed kills, and the speed limit should be lowered to save lives. And the women in this organization keep saying those dreaded words: "If it saves just one life, it will be worth it."
It is no fallacy to point out that if they keep getting their way, highway speed will eventually be reduced to thirty miles per hour. Their campaign has no limiting principle, and they think that they have an overriding moral duty to prevent traffic fatalities. So they'll keep pushing to lower speed limits until traffic is unlivable and people fight back.
So. The principle of the LGBTQUIAA2+ movement is that people should have sex with whoever they lust after. Yes, I know we call it "sexual attraction" these days, but I also believe that Mark Twain once said "never use a five dollar word when a twenty-five cent one will do." If you lust after women, you should have sex with women. If you lust after men, you should have sex with men.
What are the limiting principles at play here? Well, there is a general consensus that pedophilia and incest are icky, but that principle is in tension with other principles like "traditional morality shouldn't restrict what people do in the bedroom" or "children have wisdom that we lack."
That last principle, by the way, is why adults say with a straight face that parents shouldn't contradict their eleven-year-olds when the kids come out as queer. It's why grown-ass adults take children like Greta Thunberg or David Hogg seriously.
And this goes straight back to thinkers like Michel Foucault and Alfred Kinsley. Kinsley kicked off the sexual revolution with his studies, and he wouldn't shut up about how "children are sexual beings". And Michel Foucault... well without postmodernism, there wouldn't be queerness or a LGBTQ identity movement. Michel Foucault explicitly said that he wanted postmodernism to expand the potentialities of being, and it's not hard to see why. He was always pushing against the bounds of what was socially acceptable. He wanted to be an academic when his father wanted him to be a lawyer. He was a homosexual in a society that found homosexuality to be distasteful. He was a sadist in a society that frowned on sadism. He was a pedophile in a society that strung up pedophiles from lampposts. So when Foucault said he wanted to expand the potentialities of being, he wanted to expand the potential for people to be like him.