From the perspective of Democrats mamdani risks actually bettering the status quo for the working class. They fear this because democrats primarily represent the interests of their rich donors who have a lot to lose if the working classes conditions are bettered. Not as many profits to be made if you have to pay your workers more and can’t charge exorbitant rents. He is also upsetting the unconditional support for Israel that the Democratic party has settled upon.

From the socialist/communist perspective people like Mamdani are complicated. They can be good in that they often genuinely want to improve the conditions of the working class and often do but are limited by their decision to work within a system designed to oppress the working class. They can only do so much. Democratic socialism is just capitalism with a welfare state. Its great for the workers within the democratic socialist nation but this form of capitalism is only possible through exploitation of a working class abroad, typically in the global south.