I'm not sure you fully understand the issue. 4chan is nothing special, let alone remarkable, with regards to "getting away with" saying something. It's just a popular spot and the only one you know. I assure you that there are a myriad of forums and chatrooms all around the web that have the same sort of contents and even worse, being exchanged. The key difference is that 4chan is the mainstream, generalist forum, and a huge one at that with millions of unique monthly visitors.
Claiming that 4chan is unique in it's content reads like claiming that Pepsi is a small unknown soda brand that is almost secret.
In the old days what you're saying is true, but we're not in the old days, we're in the days where everyone uses the internet and the internet is vastly profitable. Where corporations, the state, the news-media, relentlessly seek to manipulate public opinion to their own aims. In all that, something as remarkable as the continued existence of 4chan stands directly opposed to power and everything in society that seeks to regulate and control behavior and discourse.