I see your point there. But I would also like to point out that Dumbledore was the head of the resistance against Voldemort not once, but twice. And he died when/where he did because he knew it was coming. He knew that he would have to die to keep certain others alive so that they could finish the task of taking down Voldemort. If he wanted to, he could have taken Snape with his non-blackened hand tied behind his back, but he was basically sacrificing himself.