I think their mission is worth fighting for, and it is achievable. That is, you and some people will be able to own devices that don’t spy on them and all the other benefits. There is a problem though, you don’t own most devices that spy on you…
Does it really matter if you use Facebook or Google from a Librem device? They spy on you anyways. Sure you can use open alternatives, and escape some of that form of spying. These companies have their cancer-tentacles everywhere on the internet, and it is quite difficult to avoid them for most people, even if not used directly.
If most of people still use these services, then some of your freedoms are lost even if you don’t use them. You may have freedom of speech on some sites that no-one uses, but not on Youtube or any of those other censoring platforms, where most people hang out. Sure, you have freedom of speech but no-one is listening.
The cameras that are put up everywhere you don’t own either. And since you don’t control them it really doesn’t matter if they are open-source or not. They still record you and perform some bio-metric measurements. What about all the other IoT sensors? Same thing goes there.
I think, in reality we can only try to not be the slowest gnu in the herd. Most things are outside of our control, unfortunately or luckily. To affect other peoples or companies devices we have to go the political route and I think Purism is doing a good job there too.