The problem here is they've once again proven that the rules are a complete mess that you can hardly even expect them to enforce, let alone enforce them consistently.
The AUP does not cover things like this at all, and the ToS simply says
Don't post or discuss anything illegal. You and you alone are responsible for your actions, and take full responsibility for consequences of your actions.
which may or may not be the broadest rule on the entire site. Illegal where? The US? Europe? Texas? Casper, Wyoming? Iran? Laws about drugs vary from state to state, so if, say you lived in a state that allowed medicinal marijuana, had it prescribed to you, and you uploaded a picture to FA (for whatever dumb reason), you're breaking no laws because it's not "illegal".
And if you're not allowed to "discuss" anything illegal, I suppose anyone that posts "lol I was late for work this morning and went 60 in a 45 to get there on time" should have their posts removed and get an official warning, because speeding is
illegal and therefore may not be discussed!