Well, I ask, because if you are not Jewish, you more likely than not are not going to be offended by a holocaust cartoon - unless you are deply religious -.
Kind of like if someone would create a cartoon about 9/11, ridiculing the U.S. and the people who died in 9/11. Most Americans would be offended by it, but if you showed it to a Portuguese fellow, he may or may not find it in poor taste, but it wouldn't be offended by it.
As for the reaction, well, different people react differently to the similar situations. You may have all the right in the world to pick up a stick and whack the hornets' nest, but don't birch about it when you get stung. In the case of the cartoon making fun of Islam, everyone knows how some Muslims react to that stuff. But they had to go and whack the hornets' nest because it is "their right".
But where is the common sense? I mean, you don't walk through the projects in the middle of the night, walk to a group of youths loitering in the corner and tell them what you think about them and tell them to stop, do you? Hey, it's your right as a citizen.