What is this even supposed to mean?

Let me add back in part of what you left out:

They bridle at the notion that science is actually giving us true knowledge of how the world is. And so they're always trying to police "scientism"...

My point here was that accusations of "scientism" are sometimes (note the 'sometimes') motivated by a resistance to scientific realism. Many people are fine with instrumentalism, or science as a nifty tool that pops out gadgets and gizmos we might find useful, but they resist the idea that science is really telling us how the world works.

Of course nobody should be talking nonsense about fields they don't know anything about.

And nothing I wrote indicated otherwise. You ignored what I said and objected instead to a straw man, meaning an argument I did not make.

not presuming that you know everything without having to learn or keep an open mind.

Yes, that would be the straw man. I said nothing at all implying that scientists "know everything," don't have to learn, or shouldn't keep an open mind.