Completely missing the point
Overextend good intentions drive me a little batty sometimes. Case in point. The core of racism is the belief that people of particular races aren't as capable/worthy/what have you as others. SNL looking beyond race in casting Fred Amrisen as Barack Obama, and on to actual content and capability, is the exact opposite of racism, and the exact opposite of a problem. I assume SNL gave everyone in their current cast a shot at the role. If they'd gotten Kennan Thompson to do the impression, and it was a bad one, wouldn't people complain that they'd just dropped the character duties on him because he's black? I thought Fred Armisen's Obama impersonation was really great. SNL had somebody with the skill set in house to fulfill the duties, and fulfill them well. What's the problem?
Update: Kay has a different take, and raises a good point. Thompson is the only African American on the SNL cast right now. Their needs to diversify in general are a different, larger problem, I think. But I stand by my original opinion -- if Armisen's good at the role, why worry about giving it to someone who looks more the part?