Because of their added weight, heavier gloves are generally considered safer, since impulse in physics is a measure of force over time and a padded glove increases the time over which momentum is transferred. This reduces the average force experienced by both the boxer's hand and the target.
Several commenters, meanwhile, hypothesize that "take the gloves off" may be a reference to hockey in which the players take off their gloves before fighting. That made me think I should link back to an old post I wrote about hockey fights, but all I could find was me complaining that the Capitals need cheerleaders and Justin Logan writing about hockey fights. Oh well.