Spam and content moderation are basically the same thing. In both cases it's hiding things from the user that the user didn't ask for or want to see.
Unless by spam you mean denial of service attacks. Which should probably be a point of its own anyway. It's the main killer of the decentralized internet currently.
the extra curve with spam is that it must be made economically expensive for the spammer. spam is more of a DoS attack than just content i'm not interested in.