I could easily read through any of the front page posts on Reddit, and find what I consider to be hate speech, and if I were in a position of power, I could just use that as a justification to ban the entire domain.
Moreover, it easily allows adversaries the ability to plant hate speech in forums they dislike, and then pressure the authorities to ban it.
At the end of the day, I am an adult, and I reject the notion that sites need to protect me from speech.