But, we do have freedom of speech in the US. And while that doesn't mean everyone has to give you a platform for that speech, it does mean a content provider needs to decide between being a judge or allowing everything.
Sure, Neo-Nazis seem like an easy case - nobody likes Nazis. But, what about people calling for a boycott of Israel? Or what about critical political speech? Should Cloudflare (or anyone) be in the business of making judgements about those kinds of content and if they're allowed or not?