I'm actually with Max. I think mine is set to "Ok to edit" (but I don't post pics, so I don't remember which I picked when I signed up). But I can understand someone wanting to maintain control over their image.
Some people see their photographs as a technical thing, and want advice and criticism on how to get that technical thing closer to some technical version of "perfect." But others see this as an art form, and just want to show off their vision. If someone edits that vision, the picture might be better - but it's no longer the artist's picture. Some people don't care (me among them) - others do.
Think of other media. You might write a play, and put it on, and ask "what do you think?" That invites opinions - but you might well be insulted to have someone come back with "I think it was bad, but, here, I re-wrote that last scene - it's much better now." It might be better - but it's not the playwright's work, or the playwright's vision.
For some people, that's insulting on a far deeper level than technical advice. It says that the person re-doing the work doesn't respect or appreciate the vision of the person who did it in the first place - that the original artistic vision was junk to be replaced by someone better's. Maybe it was - but such things are debatable, and some people would rather pursue their own vision than invite others to "improve" it. Even if the original artist doesn't take those "improvements," it's still insulting for some people.
The flip side is that to reach that vision, you need the tools - and someone who re-works the photo may be able to help a person learn those tools. But there's a fine line between fixing and taking over a picture - if some people don't want to risk having their artwork treated like that, I can understand and respect that.
For me, I've never shot anything that I'd call art - so I'm just looking for people to tell me how to get the exposure right.