In some left-wing circles anti-Americanism and anti-imperialism are indistinguishable. People like Max Blumenthal are the perfect representatives of this ideology.
But if you are american, those things pretty much should be the same. Anti-imperialism is not an abstract struggle, and for many around the world the US and its allies are a concrete enemy they've come by honestly.
If you live in the US, solidarity with those people means using whatever power you have internally to oppose the US's imperial actions.
The US is not the only imperialist force by any means. But particularly from inside one of these machines, it is hard to understand and act against other forms of imperialism without also assisting your own country's imperial projects.
Countries are adept at turning their own subversive and radical movements outward against their political enemies. An awareness of the mechanics of imperialism does I think lead to a "clean up your own house first" praxis and I don't think there's anything wrong with that.
They are not opposing takes. Someone trying to tell you they are is trying to sell you a fiction that just so happens to benefit Russia
But while I don't think that position is correct, I do think it's probably valuable to have some people take that stance. It's similar to the social value in having non-political conservatism that will resist all change no matter what. We'll change anyway, but having to fight for it a little will slow down the changes, hopefully dodge some of the worst consequences, maybe prevent some changes that shouldn't actually happen.
The US should be opposed. Not because we are inherently bad, but because our interests aren't everyone's interests. An always-support, always-oppose, or case-by-case stance will each have different failure modes. I think we want a mix, as unpalatable as that can be sometimes.
Apologists / accidents happen I can understand, but I wouldn't trust any individual pretending that they can do no wrong.
Nuance is important. It's just that younger lefty folks aren't used to having to use nuance on this particular topic.