MLs don't tolerate there being other commies but themselves. Got a different version of Marxism? That's counter-revolutionary and must be crushed. Advocating for something that doesn't agree with the party? Cannot be tolerated. A lot of this comes from the concept of democratic centralism, where high ranking party members can debate issues behind closed doors, but once the party votes on it, dissenters must shut up and pretend there is no disunity. It's the idea of a united front to an extreme. It inherently centralizes power and leads to lifelong dictatorships.