Herman Edwards and the Chiefs made the proposal and it had nothing to do with player safety. Per an excerpt I heard from a NFL Radio interiew with Herm, it is about achieving a more uniform appearance among all the players. It is the same as fining Portis for wearing stripey socks when everyone else wore regular socks, or flagging a player if they voluntary take their helmet off while they're on the field. They just want everyone to appear the same as everyone else, and having a bunch of hair flapping in the wind singles you out from the crowd. The issue now becomes how the players and fans would react to passing the rule, no matter what the league's reasoning for doing it would be.
The most legitimate complaint that I can see is that the rule limits the ability of the players to market themselves, and thereby making sure that the league capitalizes on their marketability more than they do, but that's a tenuous connection.