Again, WHO determines which coins are dirty? A 3rd party?
How do they PROVE coins are dirty? I.E., I don't like my neighbor - I think he's up to no good... don't accept his BTC.
I've never witnessed anybody turn down cash because it was previously involved in a drug deal.
Again, this leads to ELITISM and CONTROL.
This is just fear and noise because you are afraid of the ramifications. Any service could be as customizeable as you want. You want to only check relationship to famous addresses: Bitstamp address for example, then you could do it.
I see cash transactions all the time that do not happen because the person with the cash is a drug dealer. It happens.