/pol/, /tv/ and /r9k/ are the current uncontested triumvirate of cancer. /co/ is fucking terrible, but it's shittiness is generally contained and doesn't spread to other boards. I'd argue that /co/'s worst offence is being full normalfags, but normalfaggotry on 4chan is easily told off. Now take /r9k/ for example, you can get mad at them for derailing threads with their feelposting/MGTOW bullshit even if you agree with the notion that every roastie/chad is shit, but in telling them off, people will instantly assume you're a normalfag and turn on you. Same thing with /pol/ and /tv/.