I feel this 'movement' is in response to the ridiculous amount of attention that breast cancer has received these past few months. While men can get breast cancer, this type of cancer is socially linked to women, thus leaving men with a, 'Hey, what about us?' feeling.
To 'retaliate' men are bringing attention to our problem by doing something manly, and nothing is more manly than growing a Tom Selleckesque 'tache.
I, sadly, can only grow the Erroll Flynn and will not be participating.
Either way this ends nicely. You either get more attention to a problem, or you get pictures of some outstanding and, most likely, embarrassing mustaches that will haunt people for years to come.