If the left is all about inclusivity, why is it so full of purity policing?

Because the Left always eats its own. Nothing is ever good enough, everyone must be equally miserable and cater to the lowest common denominator; complete mediocrity and underachievement is celebrated. Obviously to them some deserve to be more miserable, just never the ones doing the finger-wagging and calling you every -ist and -ism.

To sum up, a bunch of complete losers are trying to make people feel bad for being objectively better than they are.