I find people dressed up as pregnant nuns to be offensive...yea yea, I get it, nuns are supposed to be celibate but this one did the deed it's funny ha ha ha. I suspect other costumes in a similar manner are also offensive, i.e. a rabbi eating bacon. Now, I don't run up to such people and lecture them, but I sure won't invite them to my barbecue and I probably would give them a rock instead of candy.
At the same time, this list of "offensive" costumes was clearly compiled by someone who doesn't get out much. Further, if a white kid dressed up as Hendrix and was in black face or if a black kid dressed up as Frank Zappa and was in white face, would people be angry nowadays? I hope not.
The debate will rage on...hopefully no laws are passed because while I think people masquerading as a pregnant nun are loathsome, as soon as the state is empowered to ban them then its only a matter of time before Normal Costumes are banned. Besides, I always can hand out rocks.
On a similar note, someone on another thread mentioned seeing a guy dressed as a Buddhist monk carrying a can (empty) of gasoline as a prop. Offensive to some no doubt, but funny.