As someone who's borderline ADHD and who frequently struggles with American social conventions (to the point where it's a significant stressor in my life), I'm much more threatened by people like Sarah than by Linus.
Sarah is probably more pleasant to deal with if you're socially skilled, but she demands the same thing in return, and will call you out---and apparently even go to the press---if she doesn't like how you interact with people. People like Linus will just pay attention to your actual point, and will look past the cultural subtleties of how you said something.
Every time Linus says something like, "shut the fuck up, Mauro", he's signalling that he wouldn't derail a conversation just because someone was slightly rude. For me, this means that I wouldn't need to stress over the wording of every email I send to Linus, because he's not going to care.
I'm not saying that politeness is bad---it's great if you're good at it---but random contributors enforcing politeness is toxic. Now, if I want to contribute to the kernel without getting publicly shamed on lkml, I have to be good at kernel development and at wording things in a way that's acceptable to people like Sarah. I don't think that's an improvement.