Liberals are certainly pro-capitalist, but a modern leftist wouldnt refer to a fascist or conservative as a liberal. The term is pretty much used to describe people who claim to be left leaning while still advocating for incremental (rather than radical) change, such as the modern American democratic party. It is used as a derogatory because liberals generally speaking don't have any intention of dismantling the corporate capitalist oligarchy, or implementing true socialist policies.

Even if some self-identified liberals do desire these changes - to a leftist their methods are seen as ineffectual by design, therefore further contributing to the longevity of the broken capitalist system.