Especially when online leftists throw around "idealism" as a meaningless label to dismiss ideas, and claim to be "materialists" themselves. Same vibes as "facts don't care about your feeling." They actually don't even use the correct definition of the word, using it to mean either idealists as in naive and unrealistic, or as in driven by ideals(yeah Im driven by material only, no ideas).
Engels was the first one who proposed the two camps of idealism and materialism. Later the vulgar "dialectical materialism" of Stalin turned this into a rigid division and unfortunately it caught on. In the end, intelligent idealism is still better than dumb materialism.
EDIT: This post actually shows how hopeless some self proclaimed leftists are, completely ignorant about PHILOSOPHY of all things. Is it really too much to ask to read a single page of Marx, and not parrot some other reactionary philosopher? Absolutely pathetic.
Idealism: When libs think that the way to "make things better" is to magically change how everyone thinks because akshually "action follows thought" thus if you all have the correct beliefs then reality will magically follow suit. This completely disregards how socioeconomic systems/material realities incentivize (ie. "do this or you starve lol") certain behaviors over others, and even changing how people think is impossible.
Dialectical materialism: (according to former libertarian small business owner, now anarchist small business owner, Noncompete): Acknowledging that the above is kindergarten level nonsense compared to the assertion that external material reality influences human thoughts, and due to our "conscious will"(?), we are thus able to in turn influence external material conditions, which then influence us, and so on and so on...