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.
Far be it from me that I were against Bitcoin! I am one of the few people who even owns a Bitcoin castle!
But using monero is just soo easy that even if BTC fungibility is fixed and markets would force me to return to it, I would miss the ease of life when it was possible just to click "send" and not care...
