breaking the very basic principles of open source?

No, the basic principles of open source are either the four freedoms (if you agree w/ Stallman) or the OSI open source definition. Here are Stallman's four freedoms:

• The freedom to run the program as you wish, for any purpose (freedom 0).
• The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1). Access to the source code is a precondition for this.
• The freedom to redistribute copies so you can help others (freedom 2).
• The freedom to distribute copies of your modified versions to others (freedom 3). By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.

Russians still have these freedoms WRT the Linux kernel. They can still run, study, and redistribute modified versions of the Linux kernel. There's no violation here.

And the OSI definition is similar (and longer, so I won't repeat it here).

No part of the definitions of open source or free software obligate a maintainer to work with anyone else, the only obligations are to the legal freedom of the code. Russians can still use, modify, and redistribute the software, they just aren't allowed to have maintainer positions within the Linux foundation. They can still submit code, and it's up to the maintainers if they choose to look at that code.

That said, I'm sad that it has come to this. I hate the idea of international politics interfering w/ FOSS, but I still maintain that it's 100% fine for Linus Torvalds (and his legal counsel) to make this call. So I agree with the core of your argument, that politics interfering w/ FOSS is bad, but I disagree that it violates any part of the basic concept of FOSS, FOSS maintainers should always be able to decide who they work with, and the rest of the community gets to decide if they're okay with that or if they'd rather follow someone else's fork.

The only reasonable way to avoid backdoors is to meticulously check the submitted code.

Which is the job of maintainers. Which now aren't Russian, any more. To the best of my knowledge the kernel is still accepting code from Russian citizens, ultimately not having Russians in maintainer roles isn't going to stop the FSB from infiltrating the kernel but it certainly does make it harder.

This also isn't in any way a judgement on the removed people, it's just that it so happens that if you're a Russian citizen you're quite vulnerable to wrench attacks. You could even say that the kernel org is protecting them from being used like that.

I’m actually shocked by how people are acting about this.

You see, it’s actually a really bad thing to ban devs from an open source project based on nationality over all else. “Oh, but they are state actors!!!” How do you know? Because they are Russian?

Open source IP laws operate under the jurisdiction of the citizen's country. What kind of principles do you think open source represents? Because if it's about free movement of information and global collaboration, I'm pretty sure that pirates are the group that better represents those values

Torvalds responses make clear he has spent too much time with the wrong people. Calling everyone paid actors is such an embarrassment to his own intelligence. When the linux kernel starts falling behind because of a lack of competent maintainers after banning any country that NATO isnt friends with, we will know that this is where it started and that people cheered.

in today's political landscape: genocide is acceptable and ignorable; progressives are dirty commies that you should ignore at all costs; and being russian is enough to get you kicked out of contributions to FOSS and all this comes from people who call themselves "liberal".