I've posted many critical comments on discussion lists. By critical, I don't mean necessarily negative, but probing. I'm not interested in casual yeas or nays without supporting arguments.
Knowing that my comments will be read, I do my best to explain why I liked or disliked something. If my opinion is based on a plausible read of the text, the author can't very well refute it. S/he can only say s/he didn't like my comments. His/her dislike doesn't cause me to be embarrassed of my well-considered comments.