This joke has sure spawned quite a bit of discussion!
I didn't find it offensive. It didn't knock any ethnic groups, it just knocked people who illegally enter the country - and then use services we pay for via taxes, allow businesses to undercut American jobs and salaries, etc.
Just a thought: If illegal aliens do jam the emergency rooms, then maybe Immigration should be monitoring that. Require proof of citizenship or a valid visa or passport, and have security on hand to detain those who can't provide it. I'm not suggesting that treatment be refused; that would be inhumane. But it sure would be an easy way to catch some illegals.