He lambasts the developer not for making a mistake, but for making a mistake and refusing to admit that this is a mistake. That is very different.

>we should not cause regressions

>and the corollary is that when regressions do occur, we should admit to them and fix them, instead of blaming user space

Clearly he is aware that they did cause a regression as the mailing list post he responds to would not exist otherwise. Reading these two statements descriptively renders him an idiot.

The first rule is that you don't break userspace, not that you don't make mistakes. Commits go through a process before being put into the kernel, and if yours is going to break userspace, it won't get in, so don't expect it to. You can make mistakes, but if they're found, you're expected not to say "well, commit it anyway". It's not the mistake that the violation of the rule, but the cavalier attitude.