The Athenian democracy functioned because only male landowners could be citizens and only citizens could vote.

Yes,yes. And also because internal enemies of the democracy went into 10-years forced "holiday" - one chosen every year.. Are we currently voting what politician shall be deprived of the right to be elected in elections in any "democratic" country ? You in USA don't have it, I in Poland don't have it,nobody have it.

And about "Plebs" - all worked well because of people's tribunes,your claim is complete shit. Shall I mention the optimates who were "against plebs" were supporting too peaceful politics (wanted stop expansion) and greedy, most important of them in history were bloody Sulla and Pompeius who actually were responsible for the beginning of the fall of the republic.