My 2c worth - I wouldn't want my images reprocessed without permission either, but will gladly and happily take written constructive critique.
In fact I've learned so much that I couldn't begin to name all those here on IIS who have in some way improved my imagemaking through comments.
Personally, warm fuzzy comments are nice to receive, but I probably learned more from sucking up the tough love so freely given
Having judged professional photography for the past 25 years, it's worth considering the Sh#t sandwich method when commenting. ie:
Say something nice
Say what what you
really want to say
Finish with a positive - always with the intention of improvement
This method is less likely to create offence, and may in fact build rapport.
There's going to be many different personality types here, and sometimes the simple but necessary pleasantries are overlooked when punching that keyboard.
One of the best example of this is Placidus, whose critiques are always a balance of positives backed with hard science observations.