From the previous version:

Leftists oppose the fact that the capitalists control the world. Liberals support the fact that capitalists control the world, and some of them are very loud about how they wish that control was administered more politely.

Of course liberals and leftists fight, for the same reason that leftists fight with more impolite right-wingers. We share a fundamental disagreement, an unbridgeable chasm. It’s not contrived. It’s a deep theoretical, practical, and moral disagreement, namely on the role of capitalism (or lack thereof) in our shared future.

Any coalition involving both liberals and leftists must eventually pick a side to resolve this divergence in our interests. And frankly, the only way to resolve it is to either become leftist and abandon liberalism, or devolve into yet another liberal capitalist waste of time and air.