That's not true. It's more that spam is automatic, and as such is easy to automate away. If someone replies "BUY MY PRODUCT http://product.link" on every post, that's spam. If someone is consistently shitty to other community members and generally acts like an asshole, that's someone who needs to be moderated away.

I partly agree. There's a skill and a moral quality internal to moderation, which means that good moderators will exclude the content they judge the community doesn't want without letting this judgement be swayed by their personal agenda. But bad moderation, where the moderator lacks the skill or the quality to do this, is very much a thing.