But the software licensing explicitly allows your work being used by anyone (as long as they adhere to the license). If you don't want your work to be used by entities you disagree with you can not contribute to the project or advocate for use of a different license.
This is a great point, and perhaps we do need a new popular license or set of variants that exclude certain industries. "MIT-Peaceful" perhaps.
I know very many people who would refuse to work for certain companies and in certain industries — and have rejected certain projects — but would happily contribute to something MIT licensed that would end up in those systems anyway!
The software licencing is also completely irrelevant here, nobody said that Anduril can't use Nix. The issue was that the community largely did not want them as sponsors. There is a very big difference to allowing someone (or some company) to use your software and wanting to participate in a conference where the same company is a sponsor.
I honestly don't understand what objecting to them as a sponsor does. Sponsorship benefits the project for everyone. Is the objection to both the sponsorship and their presence in the conference? Folks who don't want to engage with them at the conference can simply not engage with them.
Also AFAIK one of the conferences objected to their presence, so they weren't able to have a booth there. Individual participants are in their right to make these decisions and act on them (like that one conference did). What exactly is the outcome people want?
Sure, but that's an orthogonal point to the one OP made isn't it? Contributing to open source projects is incompatible with not wanting someone else to use your work based on ideological differences. Perhaps contributors don't think about this until they're faced with a situation that makes them uncomfortable and I sympathize with that and maybe we should start adding disclosures that say "your work may be used by entities you do not want using your work".