Use mixers if you are worried about it then! Though in my opinion this is a non-issue, a currency, that bitcoin is changes hands very frequently, so if funds that have been marked as bad or stolen gets to you, i don't feel you can be in any trouble since your address wasn't the first one to receive the stolen funds. My local currency for example is stolen from people on the streets, in their houses every goddamn day, that same money circulates, but as long as i am not the thief who stole the money, i don't worry about the origin of the paper money in my purse, even if there is a high chance it was stolen at some point.