(Might contain traces of hyperbole—still; Linus' behaviour is largely unacceptable nonetheless)
The kernel shouldn't let bad code into the tree just because the author is inexperienced. Subsystem maintainers are supposed to be a very thorough filter, so that the patches reaching Linus are up to standard. When bad code makes it to Linus, it's his job to complain about it. And based on that thread, it looks like he was complaining about it, and was not directing the complaints at the original author but at the people who were responsible for reviewing and testing the code.
It is a time-tested leadership method to make an example out of a hapless mistake-maker to keep the rest of the herd in line. And it isn't like that sort of thing doesn't happen in the corporate world; it is just that corporate dressings down (down-dressings?) don't happen on public mailing lists.
Not my preferred tactic, but in the odd world of Linux kernel development, it certainly works.
I also think that the scant, ineffectual pushback against his unprofessionalism-- especially when considering the fame and size of the Linux community-- serves to emphasize the much greater significance of his "don't break userspace" dogma.
"Don't break userspace" keeps developers from rationalizing regressions as a necessary step in the service of progress.
"Don't break userspace" allows little players to leverage Linux without worrying about a big player making problems (purposely or not) for their use case.
"Don't break userspace" keeps big players from leveraging usage statistics as a weapon against little players.
"Don't break userspace" has probably streamlined development discussion during every tenuous period in Linux' history by taking a class of bikeshedding off the table.
"Don't break userspace" neutralizes paranoiacs who would otherwise conclude that fixing a broken interface was really just an excuse for [insert three letter government agency here] to [insert insidious plan here].
"Don't break userspace" essentially disarms the entire Linux community and provides a path to a surprisingly fast development cycle.
If you think I'm exaggerating, look at the outrage against systemd where the (development community) rhetoric isn't nearly as coarse or abusive. Or even look at the discussion on the SVG list around Chromium deprecating the awful SMIL interface (which was never even in IE or Edge and never will be). You would have thought Google was was suspending habeus corpus for all the rhetoric around that decision.
That is how important "don't break userspace" is to a healthy, functioning development model. Have only that and a license like the GPLv2 and you can apparently choose the least professional communication style-- littered with cursewords and personal insults-- and still maintain one of the most successful open source communities in the world.
If Linus didn't occasionally get angry about it the people below wouldn't take it as seriously, and the kernel wouldn't as stable a target.
This is silly. Linus has written (tens of?) thousands of completely "professional" messages. A few outbursts over the 25 years of kernel development are not a choice of "the least professional communication style".
They are a beautiful thing. People may not like it, but the efficacy is beyond doubt.
If you are relying on some hacks or proprietary drivers for wifi support or GPU support (as is normal in Linux world), it might break.
