First off, let me start with saying that I’m all for CONSTRUCTIVE criticism on art work, especially if one is in the learning process. My personal opinion, and what I try to do when asked to critique work, is for every negative remark, make a positive one pertaining to the piece. 
Recently, I saw a post in a group where people started commenting on one negative thing they saw about an image. And I have to agree, I saw it as well. The person who posted the image did not ask for a critique, the comments were just made. The artist got very upset rather quickly and started attacking people. 

If you want to be an artist, and this is true for musicians, photographers, painters, and all other forms of subjective and objective substance, you will be critiqued whether you want to be or not. Regardless, if one thinks these people comenting were in the wrong, you will be critiqued whether it’s verbalized or not. You’ll have to learn to deal with it. If you can’t deal with it don’t put it out for the public to see.