[mothered]

Any brain dead vegetable can understand it, no need to reword.

You're missing the point. It's not about understanding It (you're right, anyone can comprehend It, even a 4 year old), It's the "context" of the message that's misleading.

It reads: "You should only report posts that are spam, advertising messages, or abuse". As you can see, the emphasis In on the word "only". In judging that, do you agree that the only reportable posts are spam, advertising messages or abuse?
It's pretty clear what It denotes Isn't It?