Check out some newer playgrounds. Now that they have this soft rubbery ground, all the "dangerous" stuff is back! :-) I live within walking distance of two different parks that have all four of what you named, in San Francisco.
"You don't get less hate; you just bury it underground and give them they feeling like they're being persecuted. It will make the situation worse, not better."
I think the recent rise in white supremacist violence fueled by viral media on mainstream platforms like Youtube and Twitter is a pretty strong argument against this belief. Any content on such large and familiar platforms gets to borrow some sense of legitimacy, and people who consume the content have some plausible deniability. Furthermore, algorithms that favor "engagement" create the exact constrained hate-filled extremist communities you are picturing... but then actively draw users into them from the rest of the platform!
Most apps use 3rd-party libraries and servers to show those ads, so they can be blocked at the network connection level (e.g. the hosts file) if you have control over your phone's OS. Having Android helps with that.
The apps need to handle it gracefully because they can't tell whether the ad server is legitimately down or just blocked. I've never had an app work any worse with blocked ads.