Political Ugliness

I feel compelled to comment on the ugliness that has begun to appear at McCain-Palin rallies, in which the speakers whip the crowd into such a frenzy that the members of the audience shout inappropriate comments about Obama. For example:
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And at a Sarah Palin rally, an audience member yelled "kill him" when Palin spoke about Obama and Bill Ayers.

I've been to rallies for presidential candidates, and I find it very difficult to believe that the candidates speaking do not hear these shouts. These are not hungry, riotous mobs from past centuries spilling on to the streets in search of food. These are twenty-first century Americans, some of whom are demonstrating that they believe executions to be the proper way to eliminate political enemies. Why did McCain and Palin not stop the behavior right then and there? McCain's own facial expression suggests that he heard the shout of "terrorist." Why did he grin and continue on?

If this sort of thing goes down at an Obama-Biden rally, rest assured I will comment on it and denounce it. We have elections precisely to prevent social violence. Americans must not tolerate even the suggestion of political violence.