Depending on what the contract says, you're may indeed be free to drop clients for any reason. Don't try to defend your decision by claiming they did something illegal though unless you're willing to go to court to prove it.

You are "free" to drop a client for any reason, regardless of what the contract says. You may, however, be liable. Contract law (torts) is different from criminal law. No one goes to prison for for dropping a client, regardless of what a contract says.

Cloudflare just decided to drop 8chan as a client. That's it. That's all that happened. 8chan can sue in civil court if they feel a contract was breached or they suffered damages. No one did anything illegal. No claim that anything illegal was done need be made. That's not how this works. That's not how any of this works.