Socialism

Purity testing

Yes. It is a test of the veracity of their positions, and they have been found severely lacking in a way that compromises their ability to accomplish or support anything meaningful. If I'm trying to formulate a chemical, you can be certain I'm going to test the purity of my ingredients.

that weakens movements

No. These disagreements must be hammered out, a proper line must be taken, these questions of differing opinion must be definitively answered. This is the resolution of contradictions: something that strengthens movements. If the vague, amorphous "left" took power in America tomorrow, it would be paralyzed by indecision about it's basic goals because these disagreements weren't worked out beforehand. If we're gonna have an effective movement, these disputes need to be settled. Someone is gonna have to be right, and someone is gonna have to be wrong.