I think it's an ineffective poster, because there's too much occurring and too little guidance: it's dense and boring. Perhaps illustrations would serve better than words. An illustration of what a far-left society could look like at the top of the poster, and as the eye descends the illustration gradually transforms, with the bottom of the poster depicting a far-right society. A small amount of text could be used to sharply illustrate important facets.
I originally thought it'd be more visual than wordy, but when teachers say "poster" they just mean "some information and colour".
Granted, she's probably expecting something more artistic, but I'm just not an artistic person and she can't fault me on my knowledge.