I think 4chan is an incredible, fascinating experiment, and I don't think all of it is trash or worthless, and it's true that not all boards are /b/. But it is undeniable that the overall culture is one of hostility, aggression, and cruelty, especially towards marginalized groups (not to mention the creepy sex stuff, which also pervades all boards). It's not a model for a healthy internet community by any means.
Edit: OP was edited, want to add a bit:
My overall assessment of 4chan is totally different: it is a cautionary tale of what free as in freedom on the internet actually looks like: a place where a few cynical teenage/early 20s white dudes may have a good time, while creating a culture totally devoid of empathy or inclusion for anyone else. A hotbed for lawlessness where violence and extreme ideologies fester and have real world consequences, the worst of the mid-2000s web.