blacklist coin may be removed or not used anymore

I will buy your blacklisted coins for 50% of the spot rate.
Exactly. No one would want such coins. Even when it is only the hassle of losing privacy. We then would have bitcoins that have a normal value and those with a lower value.
And this would mean losing trust in bitcoin since no one wants to receive undervalued coins. The alternative would be to use services that check coins. But if that would be a good solution for privacy?