First, you've got to accept the fact that they're probably not bad people. Maybe not even dumb or bigoted...

If your parents taught you that house cats kill more people than car crashes, and a few times a week your dad is reading the paper and tells you stuff like "tsk, you're aunt's best friend from college was paralyzed last week. A cat attacked her in her sleep. Cut straight through her hip. Her son scared it off, but they say she'll never walk again"

They've never seen a cat, everyone in their town says the same things about them. Maybe one or two people claim it's just a weird superstition, that they've met a cat and it was harmless... But only behind closed doors.

If they go off to college, see a cat, and throw a brick at it, you're going to think they're psychotic. If you start screaming at them, they're going to get angry and think you're the psycho.

Humans only know what they've learned and been taught. Plus, the majority of us are wired to trust the group consensus over their thoughts. Stuff like Fox news is their source of truth - it's what their parents and friends believed, if you have an argument and pull up their news clip and you've won.

Now as tempting as it is to respond with disgust and dismissal, you have to remember - their warped sense of truth is based around the consensus of the group. If you attack them for spouting harmful nonsense, you're not coming at them as a member of the group.

And just like a cult, they've probably been told stuff like "they" have everyone tricked, or you're one of "them" attacking them for telling the truth.

If you want to change their minds, you have to come at them as a friend.

You could ask them indirect questions with clinical answers, and find hard dispute sources of data. Just easy things that don't refute their stance, and have simple answers

Like, what percentage of people do you think are trans? It's something like .2-5% IIRC. Give that to them as a number in city or county you're in. Ask them how many high school athletes are trans - it's an absurdly low number, because surprise surprise, trans people generally don't like being called out for their gender identity.

Let them connect the dots themselves, let them go in circles trying to figure out if such a small group really has that much power, or if it's really that big a great to make laws banning them from sports when every high school trans student athlete in the country could fit in a moderately sized room

The other angle is emotional vulnerability. Tell them personal stories about people being hateful, or of how their comments hurt you personally.

Once they're open to examining their beliefs, meeting a trans person is a pretty straightforward way to make it real. Do it too immediately it might work out, or they might think (or say) "well they're not really trans, they're a normal person"...

It takes time to break programming like that - and make no mistake, this was a systemic plan now that black and gay people are no longer as acceptable to hate on as they used to be. This is exactly why the media needs to be independent - but follow the money and you'll see most of it can be traced back to a few billionaires with their own agenda

Actually interacting with a trans person is a pretty simple way to change their stance on the matter, but I wouldn't put my SO in a position before I was confident they'd be at least civil... I said in the beginning, they're probably not bad people - some people will do mental gymnastics to avoid the realization that they're wrong and have been being really shitty

Whether it's incels, bigots, or fascists, you have to be endlessly patient and give them a path back. They're all cults spreading beliefs that isolate and prevent connections outside the group - incels are a great case study, literally every single one of their beliefs about women guarantee they'll have only short, disturbing interactions with them. If they learned pickup instead of how to rant to someone you don't see them as a person and think the government should force them into sex slavery, most of them (sooner or later) would no longer be incels.

Hate the ideas, be indirect with firmly held beliefs, and (most of all) offer them a path to rejoin larger society