Dread pirate roberts used proxies, tor, he used mixers.. and even used other peoples internet (coffee shops) so that nothing can be traced back to him directly.. guess what
he got caught
it does not matter what you do in the middle to anonymise yourself, if your publicising the start(bitcoin addresses) and end points(postal addresses), given enough time a trail can be found to link the start point to the end point.
EG
mixers
if a known bitcoin address puts 10btc into a mixer and the service is known to charge 1% fee..
with enough data mining it wont take long to retrospectively check around the time of the 10btc deposit. a mixers output that totals/aggregates to 9.99btc