At one point in the history of the Wiki Community it was considered poor form to remove the comments left by a fellow editor. Time and a variety of abuses have changed this expectation.
One statement that has been made is:
Leave a comment but anyone can either integrate it, delete it, or leave it. If your edit is non-constructive, or doesn't add any information to the page, don't expect it to stay if you don't use your real name or make a few edits around here. — Where is the better version of this statement?
To that I'd add that in the same way it is encouraged that people not edit the public pages about themselves to avoid the appearance of impropriety that those with a vested interest in a particular entity described by a page employ some restrain when it comes to removing low value comments from it and either let other editors do it, or begin a discussion about it on a /Talk page.
Can we talk about it means to be "constructive"? Sometimes people use the term "constructive criticism," meaning that any criticism should be phrased in the positive. E.g.: "Service could be improved" rather than "Service was terrible." That isn't what is meant by constructive here — right? I think part of the disagreement we've been having is over what kinds of comments add to a page and what do not.
This would be something not to add, I believe (and good catch, CP).