The usual "GPL is anti-freedom" argument is that it restricts what someone is allowed to do with the source code, meaning it is less free than MIT or BSD style licenses.

I don't agree with that, but that is what the person is saying.

What's absurd, in my opinion, is lumping GPL advocacy in with two other tropes which are intended to restrict the sharing of information and knowledge, where GPL promotes it.

I see that sentiment largely coming from developers who, I think, misunderstand the freedom that the GPL is protecting.

The GPL focuses on the user's freedom to modify any software they are using to better suit their own needs, and it does a great job of it.

The people saying that it is less free than bsd/mit/apache are looking at it from a developer's perspective. The GPL does deliberately limit a developer's freedom to include GPL code in a proprietary product, because that would restrict the user's freedom to modify the code.