I wouldn't say "mentally unstable", but zealous is probably fair.

To create something like the GNU project, or OpenBSD, or Linux, takes serious levels of commitment. You really have to believe in it, and to a degree, you have to _will_ it into being. Along the way, you need to explain why your crazy idea is worth all the sacrifice, discourage those who would distract your team members, maintain your own and the team's focus through years of not actually having the thing you want in any useful form, etc, etc. You have to be an unreasonable person to take it on, and then continue it.

There are people who become "fans". They can be even more zealous than the project leader(s). Maintaining direction (aka control) of a horde of over-zealous fans takes aptitude and patience. It's easy, I think, for projects to devolve into vitriol, and denigration of those who think differently, even if it starts out from a good place.

All group endeavors are ultimately political. A group endeavor with a multi-year payoff period and no tangible rewards? It's bound to be very political.

That said, we all enjoy the fruits of their labors ...