It's not really about it being in the rules or not nor is it about censorship. It's about gaming the xp system with short meaningless replies. For instance, your initial comment of "I disagree." There's nothing wrong with it given the context of this snap (although it's my personal opinion that it would have been nice if you added more explanation in your initial comment). But lets say you go into every opinionated snap and post "I disagree" or "I agree" with an aim to boost your xp. That's what this speaking against.

Also, it's not about rules because it would be darn near impossible to enforce, similar to how it's impossible to enforce "downvote is not disagree." It's more of a request on how the community should act. It's not against the law not to hold the door open for someone, but it would be nice if people did. Similarly it's not against Snapzu rules to post short meaningless comments and covertly farm xp, but it would be nice for the community if one didn't.