>feel free to fork it and start up a parallel project without the problems you see
Most Linux distros are basically already doing this. They all have their own patchsets. It's well beyond correctness and hygiene at this point, if you actually look at the changes that are being disputed, it already falls a lot more in the "cultural differences" category.
The cultural differences that cause distro forks are debates over free-vs-libre, what belongs in the kernel vs userspace, and standardization issues, not (afaik) "we won't submit this to the upstream kernel because we don't approve of the way they talk to each other there". And I think it's very important for the core kernel devs to hold the line on those issues.
Can people actually point to instances where he was rude?
I have trouble understanding why it bothers people so much that Linus is rude sometimes. You don't have to interact with him if you don't want. You can even contribute to the kernel without interacting with him. Whatever he's been doing has been working for going on 3 decades now, I don't see a burning need to change it because it bothers some outsiders.
There's this weird sense of entitlement. People want to elbow their way into this long-running and successful project and start telling everybody how they ought to behave. They think they have the right to contribute on their own terms without bothering to understand the project culture, and think it's everybody else's responsibility to make things easy for them and behave in a way they approve of.
If you really think the LKML is too toxic and hostile, to the detriment of the project, then feel free to fork it and start up a parallel project without the problems you see. Surely your friendly corporate-style culture will attract more contributors and soon you'll have the more successful kernel, right?
Personally, I like having somebody in charge of the core of the OS who's so concerned with correctness and hygiene that he gets upset when they're violated.