Ahh yes I understand that the feedback was probably well intended but it also must be frustrating and discouraging spending hours on an illustration to see someone telling you "you should do that" or "don't do that that way". I understand that the reply was harsh but OP has the right to express their anger too... Those kind of feedback can be very disheartening. (I think I'll handle them worst than OP if it were to happen to me ahah)

The purpose of posting art is to SHOW your art, that's it. If they don't ask for criticism, you DON'T give criticism, either you like it or not. There's plenty of way to improve, giving unsolicited advice will not help as much as you think.