I'm not missing anything. I think there is a balance between abusive language and professionalism to be had, and nothing in his incensed email steps over the line. Would I write it? No, but I wouldn't quit over it either.
It takes time to be measured and restrained, and the party that never snaps at someone doesn't have the hidden backstop of snapping to keep things in line. People should want to avoid disappointing Linus, and negative reinforcement matters.
It can't be all carrot. There has to be a stick.
What happens when you only stick to professionalism? I've worked in a couple of companies that stuck to professional communication only and strongly frowned upon brutal honesty. Guess what? They're inefficient, bloated, bureaucratic messes that allow horrible engineers to get by (or even ahead). Have I learned to play in that environment? Sure, but it's a losing formula.
Likely couples, teams should learn how to fight. If they don't, passive aggressive sniping and collective failure are almost certain.