You don't need to go super far left to find convincing arguments against US foreign policy. Noam Chomsky is a mainstream intellectual after all, and he coined the phrase "consent manufacturing".

The idea that the US acts in total self interest should be presumed true in all cases, but that doesn't on its own defeat the idea that its intervention in Ukraine is good. The logical next step is to ask ourselves whether this intervention ever had any chance of changing the outcome of the conflict at all. If it didn't, and most people here would agree that it didn't, then the US' involvement amounts to wartime profiteering at the cost of human lives.

edit: I should also add, there's good reason to believe that NATO expansion is what caused the conflict, and that the west did this in spite of clear and explicit warnings from Russia