I don't think he shouldn't be allowed to work at all, but actions have consequences and the consequence of his embracing and furthering such organizations is that people boycott him.
And if I overuse sickening, this thread has also overused consequence. Yes, there are consequences. If someone wants to boycott and not buy this issue because of Scott Card's beliefs, that's their prerogative, as is spreading that message and asking others to do the same. It's also their prerogative to ask for him to be removed from the project all together and for it to be released to the public without his work.
I just, on a personal level, have a huge problem with people doing the later and will say so. I don't see anything wrong with "I won't buy a book with his product in it;" I do see something wrong with saying, "Therefore, you shouldn't be able to buy the book if it has his product in it either."