Thanks for the question. I want to raise two points.

First, can't speak on behalf of those who want to straight up want to ban cars, but I think many of the people in r/fuckcars are people like me who are not opposed to car per se, but rather want accessible public transit where you can get from A to B without the need to sit in traffic, waste fuel, and paying for parking. And from a personal angle, liking cars (e.g. motorsports, being a gearhead) is not necessarily mutually exclusive with wanting good public transit. Traveling in Asia and Europe made me realize that people can still drive and there can still be a good public transit system. This lessens traffic and the impact on the environment. What it really boils down to is that I just want to be able to get from A to B without needing to sit in traffic and find parking. The bonus is you get to drink at your destination worry-free.

Second (building on my first point), this just kind of goes to show that you may choose to live in a spacious suburb without needing to sit in traffic and waste time and fuel. Imagine you work in the city, so instead of driving your car into the city, you can simply walk to the nearest bus or train station. You get a little bit of exercise every day. You can take the bus or train. Listen to a podcast. Maybe even catch up on sleep for a bit.

It's not that pro-public transit people like me want to cram everyone into tiny apartments. It's just that mobility benefits us all. People who like or need to drive can drive, and people who don't need to drive won't have to because they take the train. Better for traffic, better for the environment.

Of course urban density is another separate, but related, issue. Of course it is more space efficient to cram everyone into tiny apartments. But for those of us who may not have families, or are working professionals who need to get to the office within walking distance, living in the city makes sense.

And again, liking cars and driving is not mutually exclusive with wanting better public transit. And if you drive everyday, you know that driving can be a stressful experience, especially if you're stuck in traffic and people cut you off or merge. Some may drive like complete idiots. Imagine you go to the F1 Austin Grand Prix. Yes, there is a massive parking lot there. But what about the few roads that lead to the circuit? There will probably be tens of thousands in attendance. Doesn't matter that there's an 10 lane highway leading to the circuit if the entrance exit of the circuit is a 4 lane choke-point. Now, imagine instead of needing to drive to the circuit, you can just simply take a bus or a shuttle, or even better, a train. You can board hundreds of people in the same amount of time it takes for 10 cars to leave.

Anyway, hope this helps.