“A commons that is uniquely exploitable by capitalists” is pretty much the size of it. I could also boil it down as “freedom zero exists”, but if you see that as a strength, you’re unlikely to be swayed by that ^^. A few angles beneath the folds:

<details> <summary>The money argument</summary> The way code generates revenue these days is overwhelmingly about a big infrastructure-owning capitalist putting up a SaaS and charging people for access. They do this so effectively that others - including the authors of the software, who typically rent their infrastructure - get only a sliver of total revenue on offer.

Nothing in the GPL protects people from this, which is why copyleft people wrote the AGPL. However, the advantage their exploiters have comes from the infrastructure, not the code, so AGPL is ineffective.

In view of this lack of effectiveness, non-copyleft people have been trying different approaches. The Commons Clause and SSPL come from infrastructure-renting little capitalists. They try to get a leg up by putting onerous restrictions on their competition. It’s not been a great success so far, as MongoDB and Elasticsearch demonstrate. Those have suffered from project seizure via forking, but that’s not always possible - new projects are coming along with licenses like this, or with similar effect, baked in from the start, e.g., WriteFreely (AGPL, but with special privileges for the original authors).

My heart doesn’t bleed for the little capitalists, so this angle doesn’t move me much, but it does sometimes get strong copyleft advocates to agree that there is something imperfect going on in their commons, even if they don’t think these license innovations are the right tool for fixing it. </details>

<details> <summary>The moral responsibility argument</summary>

When I create something, I feel morally responsible for how it’s used. Inside wage relations, this mostly boils down to refusing to work for some employers. I wouldn’t want to become even-more complicit than I already am in, say, the bombing of Yemen, by working at an involved munitions factory. I wouldn’t work at a company on the BDS list either. Liberals had an attempted boycott of companies that worked with ICE, back when Trump was in charge and keeping children in cages was unfashionable. It’s not sufficient, of course, but it’s also not nothing.

If I create a copyrightable work of my own, this sense of responsibility coalesces around who I choose to license it to, and under what terms. If it’s closed-source software, I get to decide this on a case-by-case basis, and I would absolutely refuse to provide it to certain people or organisations. We see this with musicians (those who own their works, anyway) refusing to let political campaigns or adverts use it, for instance.

Now, copyleft makes a big claim: I should discard this feeling of responsibility, because doing so leads to better software. A mortal enemy might help to improve it! Wow!

This is the basis of freedom zero, and usually finds expression in a hypothetical conflict between pro-choice / anti-choice software authors.

I used to be very impressed by this idea. For the life of me, I can’t remember why. Better software is not an imperative - we’d be fine with good-enough software. We’d cope alright with substandard software. We’d make do without any software at all, if we had to.

What about “better software” makes it reasonable to disclaim that sense of responsibility? Why are people such enthusiasts about creating a huge body of excellent software that their mortal enemies can use? Why do that instead of creating a huge body of good-enough software that their mortal enemies can’t use? Why don’t communists s/mortal/class/ and party on?

Copyfarleft licenses like the Cooperative Software License try to express the author’s convictions, in defiance of freedom zero, so they can retain that responsibility. The JSON License, with its line about being used “for Good, not Evil”, could be called an early precursor, I suppose. </details>

<details> <summary>Copyleft vs permissive</summary>

The previous arguments work the same whether the software under discussion is copyleft or permissive, but permissive software can be used to bootstrap alternatives (i.e. can be combined with copyfarleft code), whereas copyleft software can’t.

The copyfarleft commons basically doesn’t exist at the moment, of course, but writing more GPL code doesn’t help it to come into existence. Writing more MIT code might. </details>

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To talk a little about my own “journey” with this - 20 years ago, I was very impressed with FSF philosophy. 10 years ago, even, it all seemed obvious. When heartbleed rolled around, I started to experience worries about the “economic incentives” FOSS created. Sometime after I became a communist, I realised copyleft helps my class enemies more than my class allies. Now, I write permissively licensed code and dicker around with various copyfarleft licenses, trying to find the secret sauce that will fix everything. It probably doesn’t exist, of course.

So in the end, the fascism/freedom thing in the original post still makes absolutely no sense, but I do find myself sympathetic to “don’t use GPL”, for very different reasons.