You may remember during the 2008 election, MacFarlane used his animated show to mock John McCain and Sarah Palin.
In that episode (as seen below) characters Brian (dog) and Stewie (baby) toured Germany and at some point (for reasons I don't care to remember) stole the uniforms of some Nazi soldiers. After they had outfitted themselves in their new attire, Stewie noticed a small button on his uniform, looked down, and found a McCain/Palin button on the jacket - again, the jacket of a Nazi soldier.
This time it seems MacFarlane couldn't resist an opportunity to get in on Palin's latest media storm, which involves her statements about Rahm Emanuel after he called a group of people "f---ing retarded," and the Rush Limbaugh show that followed.
In this episode of Family Guy, one of the characters (Chris) goes out on a date with a girl who appears to have Down Syndrome. The ladies of The View have a reasonable discussion about the topic, as seen here:
In a response on her Facebook page, Sarah Palin posted the following:
People are asking me to comment on yesterday’s Fox show that felt like another kick in the gut. Bristol was one who asked what I thought of the show that mocked her baby brother, Trig (and/or others with special needs), in an episode yesterday. Instead of answering, I asked her what she thought. Here is her conscientious reply, which is a much more restrained and gracious statement than I want to make about an issue that begs the question, “when is enough, enough?”:
“When you’re the son or daughter of a public figure, you have to develop thick skin. My siblings and I all have that, but insults directed at our youngest brother hurt too much for us to remain silent. People with special needs face challenges that many of us will never confront, and yet they are some of the kindest and most loving people you’ll ever meet. Their lives are difficult enough as it is, so why would anyone want to make their lives more difficult by mocking them? As a culture, shouldn’t we be more compassionate to innocent people – especially those who are less fortunate? Shouldn’t we be willing to say that some things just are not funny? Are there any limits to what some people will do or say in regards to my little brother or others in the special needs community? If the writers of a particularly pathetic cartoon show thought they were being clever in mocking my brother and my family yesterday, they failed. All they proved is that they’re heartless jerks. - Bristol Palin”
Seth MacFarlane is a comedy writer, and while that is no excuse for his actions he has the right to create whatever he wishes.
Ultimately the market will decide if his or any other brand of humor is acceptable, because quite simply if people do not like what he has to offer, people will turn him off.