It could be. That's why subjective interpretation and reasonableness are concepts.

there is no single "best" and no single "community"

There is clearly a single community by any reasonable definition – diffuse though it may be. The role of a set of guidelines is to establish what behaviour that community has generally decided is acceptable or not acceptable. We accept this kind of moderation guideline all of the time.

maybe just replace it with "dont be an idiot, respect others and assume good intentions".

Yeah, that's basically what it says in a little bit more detail, and with a few more examples. So where's the issue?