There's standing up against racist slurs, and there's attempting to ensure that nobody can ever say anything negative about a black person for fear of being accused of racism.

Obama's presidency has generally been a good thing - but in this case, Obama made a comment that was highly offensive to people with disabilities, and he deserves to be called on it. There's a long tradition of newspaper cartoons actually being vaguely related to current events and expecting you to keep up with them in order to understand them.