https://www.cloudflare.com/en-au/website-terms/
Hackernews can do the same to your account on their site.
https://www.ycombinator.com/legal#tou
It is what you agree to when you use someone's service.
Pretty much every online service has this clause buried away in their ToS.
Twitter deplatformed an ex-POTUS and he went and built his own platform.
CloudFlare is well within their rights to do so. It might not be "right" to you, but it is their right to do so and they pulled the trigger on KF.