You know, a simple tag under your name that says: Editing Allowed, Ask First, or No Edits, Please would cure this problem. I have always been of a mind if you post in "USER CRITIQUES," you open yourself up for edits unless otherwise directed.
Yes, on the face of it, reasonable.
However, critique is one thing but copying and messing with an image
is a step rather far beyond.
IMO, and I don't think it's right touching without asking. It's a nice ego trip to take an image and exercise better skills on it, but that's personal ego and glory and eff all to do with the poor mutt being ripped. Verbal advice can be nice (and is usually neutral), but humiliation never. Unless it's your bag, of course, but are we that broad a spectrum here?