People have suggested this before. A bad actor then just takes 100 illicit bitcoins and sprinkles them in random amounts across many addresses, 11 to himself at another address, 6 to a non-profit, and 14 to you. You are now indistinguishable from the bad guy.
I can't say I would complain if thousands of dollars was given to my address, but you are right... it would represent a difficult problem for enforcement and creative people would come up with clever workarounds.
