1. I agree about the "you're free not to use it" line, but I frequently find that documentation can seem comprehensive when you're evaluating something, but as soon as you get deeper into the weeds, that's when the shortcomings reveal themselves. And telling someone to "help them" when they themselves are looking for documentation to get help? That's just laughable. I sure as heck wouldn't want someone who can't get my product to work to be submitting documentation PRs.
2. This is just snide. Refusing to help someone because they're expressing frustration is simply spiteful. You have no more information than the rest of us about what was actually asked, so implying that the author "had it coming" seems uncalled for.
3. Then you're not very familiar with the OSS economy, are you? There are frequently paid support plans available for major OSS projects.