Good feelings are bad because they are a warning sign of bad faith criticism. While honest feedback is unquestionably important, there are a great many people who criticize more for their own self indulgence than for the sake of others. It's a seductive enough trap that even well meaning people might wind up giving bad feedback simply because it feels good to criticize, all the while justifying it as helping someone who is not, in fact, left any better off.

When criticizing, it helps to have a clear reason why. It may be a good faith attempt to help the other person, or because their actions affect some other thing they are contributing to, or because their actions have unintended consequences for someone else. Regardless, there should be some benefit beyond one's own gratification. If you catch yourself enjoying the act of criticizing others, it's probably a good idea to doublecheck your motivations and results to make sure that it's actually for someone else's benefit.

You must be one of those folks who don't like code reviews then. Good criticism is a lot of work, and it can be immensely helpful.

> Good criticism is a lot of work

Bingo - Good criticism is a matter of considering how it will be taken, because you aren't feeling good about the criticism itself, but rather the results you are trying to achieve. Bad criticism is enjoying the criticism itself.