Well-groomed beards seem to be fashionable these days, which I believe means they wouldn't detract from the professional image. Personally a 1/4 inch beard is part of my "residual self image" as described by Morpheus in The Matrix. My biggest concern is the amount of subjectivity in who should and should not be allowed to grow one. Some dudes can't grow decent beards and shouldn't be permitted to walk around with scraggly-looking garbage just because the hairs are within a certain length. Where is the line drawn? Does a chief pilot become an official beard judge to tell individual pilots yay or nay? From a management perspective it's better to just say no to all.