The "normal" type of censorship in the existing consensus rules is content-based with the goal of enforcing a subjective moral preference. I don't think censoring spam is worse than that.
For example, the existing consensus rules censor transactions that try to create more money in the outputs than is consumed in the inputs, without proof of work, because node runners subjectively prefer a network where no one can do that, where the ability to inflate the supply for oneself without working for it would be immoral, a type of fraud. So we censor it. Personally, I don't think it is wrong to go down the morality police route; I'd like to do it even more by policing the network against spam too.