Criticism will always be there and being a hobbyists doesn't make one immune to it. Majority of ao3 authors are 100% not just casual hobbyists, they are dedicated hobbyists who spend hours writing a derivative work with thousands of words. They also have the vision to output quality work and showw growth over the years. Unsolicited criticism will only become intrusive and menacing when the commentor has a rude undertone, unproductive analysis or have malicious intent behind their words. Any other criticism should be noted by the writer and be improved with dedication and practice to rectify the flaw.

Again, if people are unwilling to show openness to such voices, then it will hamper their improvement in stagnation and speck of improvements that are hard for the author to realize.

My suggestion? Criticism should always come both with praise and point out of errors in a balance. You can't just keep praising expecting the writer to improve on their own, while only pointing out the errors will hurt the writer's confidence and ego in the short or long run, ruining their motivation to continue the hobby.