The only reason you would ever be worried about receiving "bad" coins would be because of some legal framework that makes such coins possibility "bad". The exact same legal framework could make 100% of Monero's coins "bad". And you're back to square one.
Having to spend contraband coins in a public blockchain would feel awkward, a private chain suits the use case much better.
Bitcoin plus this (or any number of other extensions)
enables Bitcoin to be
used in a completely private manner. I don't see any difference between Bitcoin with these easy extensions in how it is used, and Monero.
That and there is no difference in the level of "contrabandness" between contraband coins in a public blockchain and a private chain that is declared to be entirely contraband.