Blacklisting doesn't have to be a feature of a blockchain. It's enough if most countries decide to make it illegal for anyone to spend coins received from a blacklisted address. It's not easy to enforce of course, but people would be afraid they get in trouble if they're ever deanonimized, and businesses could be required to report their trades, just like taxes.

This will force creation and use of wallet reputation checkers for most users of cryptocurrencies. Mixers will not want to be left holding all the blacklisted coins, since that causes them financial loss. Therefore mixers will launder coins at a very high premium (lemon market) and compete on developing their own systems for reputation checks and escrows to reduce their risk of being left with coins nobody wants.