I know plenty of Americans who will happily listen to unaccompanied singers when they find them. Granted, there are probably fewer instances of unaccompanied singing by individuals overall except possibly in Appalachia and in African-American communities. We've got a larger proportion of landlocked area; shanties aren't that big a sell.
I always though the division was that some people are jerks and some are not, and some jerks happen to play instruments. There are also jerks who sing along loudly enough to interfere with the performer, so it's not strictly an instrumentalist problem.