I think it is a valid concern. BitCoin can been seen as cash (anonymous) and is much more convenient to transact with... I'm pretty sure this will be one of the major argument used as soon as the governments will wake up. We better be ready with strong responses.
Isn't the response contained in what you just said? Anything done with BC can be done with cash. Despite the possibility of laundering, we've been able to live with cash.