Hitler is ok to use for good

I don't usually post about politics but this post at Scripting News and I feel compelled to point out something. Firstly the post from Scripting News posted on 6/27/2004:

Bush is an awful leader, but so far there's no indication that he's comparable to Hitler. But he's running an ad with pictures of Hitler, between pictures of John Kerry, Al Gore, Richard Gephardt and Howard Dean. How could someone want to win so badly that he would be willing to do that? What are we supposed to think about this? Does he know that Americans have families who were murdered by Hitler? Is this what compassionate conservativism is? What does he stand for? This should be question #1 at the next Bush press conference

Now, here is a post about the very Moveon.org ads that are featured in the bush ad, posted on Scripting News 1/5/2004:

People who support Bush apparently don't like the MoveOn.Org comparison of Bush to Hitler. I haven't seen the ad, but I don't find the idea offensive. It's about time people outside the blogging world started ringing the bells. Wake up. They're taking the Bill of Rights apart. Get your priorities straight. An ad with some imagery you find offensive is nothing compared to what the Republicans are doing. We live in amazing times. The professional press isn't covering the laws that are passing in Congress and being signed by the President.

Most people will agree that the use of images of Hitler in any political advertising is not a good idea, but it looks like Dave only finds it offensive if he doesn't agree with the candidate.

Why is it ok for a Democratic organization to use offensive imagery to attack the President, but it is very offensive if the President responds to the attacks and tries to turn them around?