The problem is that Linus has transformed a technical disagreement into the language of a breach of trust. There is no argument that Eric can offer to demonstrate that he weighed the factors and determined breaking userspace was the right call (it's certainly a call commonly made in kernel development, even by Linus himself on occasion!). And Eric can't argue fully because he feels a duty to his users to continue the rest of his work, which is now being held hostage. (Should he refuse to concede the point, then permanence kicks in. It reminds me of certain teachers I had in high school who I still believe were wrong on the facts but the threatened social consequences for pushing the point weren't worth it.)

So fundamentally we have the same practical problem as with personal attacks: that it's bypassing what should be a discussion on technical merit. Maybe Eric's feelings aren't hurt, but it's still not clear we're building the best kernel we could.

If you read the rest of the chain til the end, Linus acknowledges that occasionally userspace has to break. He mentions security issues and extremely old code that provides no other option but breaking it, but then suggests that this was not one of them.

> () Yes, there are exceptions. We have had situations where some interface was simply just a huge security issue or had some other fundamental issue. And we've had cases where the breakage was just so old that it was no longer fixable. So even rule #1 can sometimes have things that hold it back. But it is very* rare. Certainly nothing like this.