Three things:
1. Cancer is curable. Obviously not in every case, but many, many people who have been diagnosed with cancer have been able to overcome it. I have never heard of anyone being cured of retardation.
2. "Retard" is commonly used in a defamatory manner, to infer lack of intelligence. You don't hear things like, "Smooth move, cancer patient." Before you wade into the waters of comparing "cancer" as a derogatory term (as in, "DWill is a locker room cancer") please note that, in this respect, it is the cancer itself, and not the cancer patient that is being compared.
3. It is a bit of a leap to assert that disdain for Fisher's actions equals disdain for his daughter or her condition. These are two separate issues that you seem to be unable to distinguish. I don't remember anybody making a joke about Fisher's daughter. If I'm wrong, feel free to enlighten me.
Personally, I don't care about Fish. He did what he did, and I don't care if hos motivations were pure or not. He struck a deal with Larry, so that was that. It's a little funny that there are still some hung up over that whole situation. A lot of it is probably frustration with no movement on the trade front.
Hope that clears it up for ya!