Misinformation and harassment also exists on smaller platforms, it is a matter how to deal with it. Smaller platforms usually have a more tightly bound user-group and moderation, so it is detected and prevented earlier. But this also means that someone you trust in the group needs to be the moderator or have certain privileges.

So, effectively it is more work per user to manage smaller groups than larger ones -- which is fine, if you find people who want to do this task. Another approach might be a community driven model -- where detractors could be ostracized. For very small groups this might work out well, but as the group gets larger, the potential for misuse rises also.