Actually it is. Genocid is the methodical destruction of a human group.
In Gaza. We now know that their is a volontary ethnical cleansing that is helped by the dehumanization of the population. Added to that the Israelian assertion that the population of Gaza is not innocent and that every terrorist must be eradicated.. you have the germs of the genocide which is happening under our eyes.
This is a genocide, an ethnical cleansing and a colonization. This must be denounced as such if we want to end this war and juge the culprit.
Authoritarism can indeed be capable of genocide. Weither you can call that leftism is more debatable on a political bases.