4chan is moderated to the hilt.

It's moderated but far more permissive than the internet at large. Also, maybe they're really good at deleting complaints about the moderators?

It's not really comparable because their boards have a limited number of active posts and the bigger boards get so much traffic anything is gone within a few minutes. So if you complain about something and they don't respond within the hour, it's gone anyway.

Still they have big problems with spam, ddos attacks and moderator turnover and that is after they delegate the bigger problems to /b to be mostly ignored.

Yes 4chan is a mess, but I'm glad it's there.

Though 4chan does have moderators.

So why is there so much racism, doxing, and other horrible behavior? Or are only some of the boards moderated?

All boards are moderated in a completely different way. Most of the boards have a pinned post with the rules. Most moderation occurs stealthily.

Also, racism and doxxing are not comparable at all.

The double-edged sword of not moderating based on racism and other undesirable behavior is that your job as a moderator is much easier, but you have the terrible reputation that 4chan has. I am personally fine with boards that allow pretty much everything other than CP and other illegal content. I think this is how a number of chan boards operate.

Do they both not belong to "horrible behavior?"

Is this "If you can't beat em, join em" Nazi edition? Half the challenge of the other boards out there is keeping the waste of molecules that constitutes 4chan away.