I get what you're saying, but the idea that a license forces you to do something seems a bit of a skewed description. Linux being GPL licensed doesn't force me

I get what you're saying, but the idea that a license forces you to do something seems a bit of a skewed description. Linux being GPL licensed doesn't force me to do anything. If I want to use linux, I can. If I want to modify linux, then some rules kick in. But it's still opt-in, because you're not being "forced" to leverage the fruits of someone else's labour in the first place. And if you want to leverage others labour, all that's asked is that you make your labour available for others to do the same with. Which is, I guess, what I meant by "ideological". It seems like they are not just sharing some work they've done - they're sharing work that was inspired by a philosophy, and values they're trying to get others to adopt. Which is why it seems like a prime candidate for GPL licensing.