Leaving aside the outright abusive, probably nothing. But how excited would you be to receive in your inbox "Your [beloved project] didn't solve my pet problem

Leaving aside the outright abusive, probably nothing. But how excited would you be to receive in your inbox "Your [beloved project] didn't solve my pet problem the way I wanted! This software sucks and the devs are lazy bastards who don't listen to the community". Then imagine getting one of these a month, a week, even a day if your project is very successful. It's of course nothing like actual abuse or threats of violence but it's an emotional toll that I certainly wouldn't want to pay. I have better things to do with my life.