It's not like people condemning the choice of the name are unable to find the humor. We do find it. We are briefly entertained. Then we pause and ponder. Is it a good idea to use a negative stereotype in a joke? Don't we run the risk of confirming the stereotype even more?
We then find out that our answer to that question is "no". And we bring up the issue with other people.
There is no "inability to find humor" at play here.
It's called stochastic terrorism, and a society built on top of terror and racism would probably tell you it's "actually a sign of cognitive flexibility and social intelligence."
I had the same gut reaction as you. I was going to defend the joke as not being racist. Until I thought about it for a few minutes, and came to the conclusion that it's obviously racist. Whenever you have a gut reaction like that, you NEED to look deeper.
If the joke itself is racist then a typical reaction would be to consider it less funny.