I would interpret “demonizing” something as meaning misrepresenting it in a hyperbolically negative manner that may even involve completely constructed criticism.

I don’t think that highlighting authoritarianism in past social experiments constitutes demonising them. You’re right that there were significant successes in these projects, and also that they weren’t perfect. If we don’t properly acknowledge the ways in which they went wrong, can we really hope to do better in the future?

I don’t see any way in which the people you’re replying to are being at all revisionist.