1971ti:
Offering feedback about how the story could be altered or extended into further parts is good. Writing that the author should not have a character doing something because you do not agree with it in the real world is not appropriate or helpful.
I disagree. I appreciate all comments, but really don't want to be told how I could alter or extend a story. That story is written, finished, and I am not about to alter it. If it is to be extended to another part, I already have an idea of how I want to do that. But what I do appreciate is a sincere comment that a reader would like to see it extended.
As far as comments about what a character might do in the real world, I think it depends on the spirit in which they are given. I try to make most of my stories realistic, and find it helpful to hear other perspectives. I can't relate to all of my characters at the same level, so I like to get feedback about how believable they are, as long as it isn't a moral judgment.