It's unethical, without a doubt. As described, it's not even about segregating different audiences, but about sequestering and silencing specific people, yet k

It's unethical, without a doubt. As described, it's not even about segregating different audiences, but about sequestering and silencing specific people, yet keeping them engaged at the same time, perhaps to be able to continue to show them ads and keep up the platform's KPIs. In a way, that'd be quite similar to dating platforms creating fake profiles to keep their members engaged, which I doubt anyone would consider ethical behaviour. If an online service doesn't want certain types of opinions, ideas, or people on their platform, that's absolutely fine. Just tell them, so they can take their business elsewhere.