You say confirmation bias, I say principles. The difference is, I don't feel guilty... Fake news! It really is. And real progressives should be ashamed of themselves for giving any credence this shameless pandering from the same old warmongers they used to rail against.
And here is part of the issue. You call it "the usual tripe", and blast people for "giving [it] any credence". That is to say that (whatever sources you are talking about) you completely dismiss it out of hand, which is dangerous.
As an example I spoke to one guy who was convinced that the vast majority of Muslims wanted to kill all non-Muslims. He had never spoken to a Muslim about their religion or their views. When I pointed out that I have known many and none wanted to kill anyone, his response was "well they would say that, wouldn't they". He was completely closed to the idea that any Muslim could be a good person, and no evidence could convince him otherwise. In his view I had been brainwashed by the PC culture, and anything I said was dismissed out of hand as lefty propaganda.
As soon as you dismiss any source out of hand you create a dangerous situation for yourself, closing your mind off. You read more sources which confirm your viewpoint, and less which disagree with it. This is textbook confirmation bias, and can lead to dismissing provable facts just because they don't fit your own world view.
I'm not having a go at you, or anyone else. As I said, I try not to let it but I know that it affects me too. It's a part of human nature, but it's a part we should at least attempt to minimise.