"What it comes down to is that laughter makes people more comfortable. It relieves tension, covers uncertainty, grounds us in the face of the unfamiliar. The pressure release valve of humor is a necessary and valuable thing. It doesn't exist in a vacuum, however. When the privileged laugh at the marginalized, they make themselves comfortable at the marginalized's expense. Their humor is, quite literally, oppressive.
"As a trans woman, when I'm told, 'Come on, lighten up!' 'It's just a joke!' 'Learn to laugh at yourself,' what I actually hear is, 'Your existence makes me uncomfortable. Please render your body and your lived experience more palatable for my consumption.'"
-- Joli St. Patrick, 2015-05-31 (if you read the whole thing, it makes the point ad the context clearer and probably addresses the first few reactions that come to mind, and it's only a few screens long)