"By Design" a desirable resolution?

Keith Stobie (a test architect on my team) made a comment recently, along the lines
of:

"If testers aren't getting some bugs marked 'by design' and 'no repro', then they
are probably being too conservative in their bug filing."

This intuitively makes a lot of sense to me; the philosophy of only filing clean,
certain bugs seems prone to unnecessarily missing issues.