The author has every right to stop accepting the uncalled for abuse from users and drop development and support. I hope he can direct his attention to things that give him joy instead.
Please read his comments. He is overwhelmed and I wouldn’t be surprised if he even felt abused. Users (especially free tier) can be (more often than not) nasty towards developers.
If it he doesn't want to "feel abused" maybe he should not have been shipping people's contact lists off to a third party without their knowledge or permission while claiming to be a privacy-oriented application?