You give people something cool for years at no cost and now they're pissed that they have to compensate you for your labor.

The way that people value software these days is completely insane.

People writing you hate mail are bad clients that you don't want and you can feel free to ignore them.

Also watch this video that was doing the rounds on HN a couple of years ago: https://www.youtube.com/watch?v=jVkLVRt6c1U&t=54s

Your app looks neat - I'll go try it out.