First, I was wrong in linking libertarian with GPL, I was thinking of permissive licenses like MIT. GPL is a CopyLeft license, in that it forbids proprietization. MIT is more like, do whatever the hell you want, you just can’t sue me.
The joke should have been “Libertarian MIT License or DIE!”
I think MIT is actually a pretty rough license, because it allows someone to come along, take the open source work, add anything, or virtually nothing and then start selling it as their own while keeping any new code secret… when they got it for free. I’m mostly against that, but there are people who believe strongly in that type of license.
I’m more in favor of GPL like licenses (not prescriptively, but preferentially) because they force the work and its derivatives to be shared by the community, for the work to continue to be open source.