I don't think their heads are what's empty. It's their hearts and souls. Empty. Devoid of any valid honesty.
But they're not stupid per se--they're smart enough or crafty enough to maneuver liberals into high positions in our society. They're experts at manipulating public opinion, and at pulling the wool over the public's eyes.
To call them "stupid" or "empty-headed" puts everyone at a disadvantage: this is a sly and clever enemy we face on a day-to-day basis, and we should not underestimate the evil of which they are capable.
In truth, I think this has been, and continues to be, one of the Republican Party's greatest shortcomings: underestimating the enemy.
And enemy they are--as much (at least) as the AlQaeda. More subtle, perhaps, but in many ways at least as dangerous.