I will play the devils advocate here...
I've browsed 4chan every now and then during the last year I will totally disagree with you.
If anything, the post quality is deceiving, not immediately apparent. I couldn't understand at first, but then it became obvious.
99% of the posts are striped from any real content, they are irrelevant single words, offenses, f*ked up puctures, funny pictures, etc. But then, in 1% of the comments lies the real value of 4chan.
I've seen very insightful comments in there. Many topics that would be taboos on pretty much any other place on the internet are discussed there openly and with innovative views.
I'm not sure about the purpose of the huge amount of useless fluff, but if you want to get the real content you need acknowledge that crazy people will post tons of stupid things while serious discussions take place.
If you have a totally new way of looking at a subject, if you expose it to a place where your identity is valued, you will for sure get it damaged. So everybody refrains from posting potentially controversial opinions. Going the opposite direction and totally remove identity ties, will attract trolls, but you get the real stuff, what people really think, no bullshit, no political correctness.