The developer doesn't owe us anything, but if they're creating an online community like Discord there are inherent responsibilities that come with that. If they don't want to moderate, then they shouldn't create a Discord/Matrix/Whatever server.
Just like how even if the developer doesn't owe us anything, that doesn't mean it's fine for them to push malware as an update to their previously fine code after they've established trust.
Depending on something isn't necessarily tied to how many alternatives there are.
For example: I use a heavily configured qtile setup on my desktop. I'm depending on that setup working every time I turn my computer on. Sure, I could switch to i3 or sway or Hyprland, but that would take a considerable amount of time and effort. In this case, I'm depending on qtile working for me, so I can get work done instead of messing with a bunch of config files. The only time this wouldn't happen is when one solution can be a completely (or almost completely) drop-in replacement for the other, e.g. how sway claims to be with i3.
This is especially true with tiling window managers, where people spend many hours configuring setups to behave how they want. Moving to a different alternative isn't exactly simple.
To your point about FOSS: chrome and android may not be FOSS, but as much as I dislike it AOSP and Chromium definitely are, even if Google controls the repos for both. Your definition is a slippery slope because by that definition software like Ubuntu, Manjaro, etc. also aren't FOSS because the repos are controlled by a single company.
To your last point: telling someone else they shouldn't use a piece of code for the same reason you don't is also perfectly valid. It's not like it's an order, they don't have to follow it. People can choose to agree or disagree with you if they want. Ultimately, the decision to install software in Linux lies with the user, and the most any online opinion can do is give a persuading or dissuading argument. Just like I could say, "don't use this software, it's built on some old deprecated library that will probably break in a month", I could also say "don't use this software, the main dev is a bad person because xyz..." and it would still be up to the user to make a decision. If you don't mind disagreeing with the author of software you use, that's fine, but not everyone is like that, and that's also fine.