Pick a social cause and you will often find a Hollywood celebrity speaking out. Gay marriage has Brad Pitt, Darfur has George Clooney and the environment has Robert Redford or Leonardo DiCaprio.

Gun control? Not so much.

Most of Hollywood's biggest action movie stars have remained silent, so far, on the divisive issue following last week's slaying of 20 young children and six adults at a Connecticut school. And pop culture experts said it's not hard to see why.