It requires you share the code with your users/the people you distributed derived works to for no additional cost. You can still charge money for the software, but you can't charge an additional fee for access to the code. You also give them the right to share it how they seem fit, so they could share it (the code, not necessarily trademarked things like names or artwork/assets) for free, share derived software including the code for a free or a fee, or not share any derived work at all.
Both "socialist" and "libertarian" have definitions that not just changes within a country, but basically every country has its own understanding of the terms (just like what people in the US would consider "far-left" is basically "center" politics in many places in Europe).
Labeling something "socialist" or "libertarian" in a diverse place like HN probably harms more than it does good, as everyone will read it differently and have different takeways.
To use entirely different terminology, I think people are just way more laissez-faire about software issues these days. Realistically, most software runs as a service now, and people are generally I think more happy to be more pragmatic rather than idealistic. I think GNU was generally aligned to the mainstream 'tech hacker' outlook in 2002, but it isn't in 2022.
The resistance to surveillance, the kind of 'prepping' mentality of running everything yourself, never using third-party services, and sticking with older working ideas over trying new things, those are much more libertarian than socialist, going off literal definitions of individual liberty over collective society.
It requires you share the code with your users/the people you distributed derived works to for no additional cost. You can still charge money for the software, but you can't charge an additional fee for access to the code. You also give them the right to share it how they seem fit, so they could share it (the code, not necessarily trademarked things like names or artwork/assets) for free, share derived software including the code for a free or a fee, or not share any derived work at all.
You can read more here: https://www.gnu.org/licenses/gpl-faq.html