So new user but long time reader and I want someone to explain how these analytics firms are alleging that coins may be tainted solely based on being connected to a dark net marketplace? The fact is in the early days of dark net marketplaces when few bitcoin exchanges existed (aside from MtGox) people routinely bought bitcoins on dark nets using money pack cards.  The purchaser of the bitcoins committed no crimes as he is not considered an unlicensed money transmitter, while the seller is consider one. 

People also used dark net marketplaces as mixers themselves transferring coins onto them and then off again.

Under these two scenarios the coins are not involved in criminal activity, however, it seems these analysis firms claim they are criminal solely because they have some connection to an output from a marketplace.  Am I correct that this is what they solely base the taint on when it comes to coins surrounding dark net marketplaces?