You're missing the point. It isn't "oops, we don't know how to block people and communities." Their attitude is "People who disagree with us do not deserve to have a voice at all."
They aren't content to just "not visit those communities or block those users". They're only content if those viewpoints are completely banned.
It isn't "If you don't like it, don't read it", which is what a reasonable person would do. Their attitude is "If I don't like it, nobody should be allowed to read it."