People cannot post whatever they want on 4chan. On boards such as /g/, and /sci/, any off topic discussion is banned, including blatantly racist content. Other than that, there is free discussion that can be quite enlightening. And just because you choose to use a website does not mean you agree with the fringes. Just because you're a reddit user, and reddit has gore subreddits, are you into gore?

Older than that, here’s a take from 2004: https://www.penny-arcade.com/comic/2004/03/19

reddit is the same thing. not all of 4chan is bad. not all of reddit is bad. but there is bad on both. it has nothing to do with the website it’s the format

The whole reason 8chan was created was because they were kicked off of 4chan for disgusting behavior (specifically doxing/harassing game journalists)

I think it's also that unmoderated forums become a magnet for people who want to spew hate, rather than anonymity inherently leading regular people into such behavior (though maybe the former causes some of the latter).