I wasn't worried about the Swift Boat ads also. But anything that can be twisted into being racial politics is a more tricky, explosive situation in my view. Some independents/soft repubs might feel a guilt trip--that if they don't vote against it, they, by extension, are racist.
Oh well--if it works again, great, but if it doesn't, hope the worst it'll have is zero effect. Like the updated "Daisy" ad the dem side ran not long ago.