I have been maintaining open source projects, and really: users of open source projects suck. They get your work for free, but it's not enough; they have to be assholes on top of that.
I would say it's more the case that the users who suck are both the loudest and also seem the loudest. If you get 10 people saying thank you and one person cussing you out, it might still ruin your day. And of course a lot of people just quietly use the thing and are happy with it, and you never hear from them at all.
