Why do people sometimes get so upset about political cartoons?

I am an editorial cartoonist for Southern Utah University's student newspaper, I really enjoy my job, they basically pay me to have an opinion. It's also great because every once and a while some people get totally offended and all worked up about a cartoon I've illustrated. Why can't people just remember that first off all, it's only my opinion and second, most importantly -It's just a cartoon!!! Any thoughts anyone?