Imagine how much extra racist Yik Yak would have been during the summer of 2020 and today during the Gaza war
Silencing people isn't going to make them stop thinking things and preventing discussion won't make them Good(TM) people.
The entire internet doesn't need to be sanitized.
The goal is to encourage actual communication.
Forums didn't have the same issue because they were often single/few topic websites and you could just aggressively remove everything off topic.