Technical criticism, even when direct and unpadded, is not rude. Indeed, it can be a form of flattery: the critic is saying, by implication, that the target is worth taking seriously, and is worth spending some time on. That is, the more viable it would have been to simply ignore someone’s post, the more of a compliment it becomes to take the time to criticize it (unless the critique descends into an ad hominem attack or some other form of obvious rudeness, of course).
— Karl Fogel, Producing Open Source Software
While I understand and agree with the sentiment behind this post, it’s important to realize that how you phrase your criticism can make the difference between it being encouraging or discouraging.
BAD: Your foo on line 44 is wrong.
BETTER: Please fix your foo on line 44, you probably want to do bar instead.
BEST: This is great overall, but on line 44 please do bar instead of foo, because baz. Thanks, this patch will be a real help!
If it’s someone you’ve worked with for years, option 1 might even fly. If it’s a new contributor, you probably want to go with option 3. You should always take the time to be nice, not merely not rude.
Technical criticism can also be rude. The point Karl is making is that it’s not inherently rude.
I think different communities come to different conclusions on what sort of tact filters are required in their world.