It is absolutely desirable. The point of a SE is not to be a discussion forum, but to be a knowledge base. As new viewpoints come to the site, they should be continually added to old questions, which means edits and answers and comments and votes and whatever other activity.
Working on old questions doesn't stop anyone from submitting new ones. Use a different view if you don't want to see old questions - I usually stay on the "newest" tab which accomplishes that.
For my part, I only find the churn annoying when it looks like someone is looking for something—anything—that they can edit to work towards the Strunk & White or Copy Editor badges. The edits that make me suspicious are the ones that just move the quality of the question "sideways" so it says the same thing differently instead of "up" so that it's clearer/punchier/more interesting.
Otherwise, I don't mind the churn. I sometimes wish there was a tab for "active questions that aren't just being copyedited", though.
An important part of SE is that old answers are the benchmark, the ones we point people to again and again. As we grow larger and have more volume we will see the same question again and again. Instead of answering those questions we should be pointing people to the old one, closing the new one, and go on.
Thus it behooves us to ensure the old question and all answers are as streamlined as possible.