I think we can all agree that it doesn't matter where a Bitcoin was before it was in your wallet, but your employer or government certainly might not understand that yet, and it's unfortunate, but sometimes you have to play in the bounds of the rules in which you live.
What makes you think your government will think Bitcoins coming from a mixer are better than your own Bitcoins?
Problem is that there is no universal standard for ''clean'' coins.
That's because it's impossible.