> Imagine what would happen if the fuzz link an address a few levels up the chain to a drug transaction. How long can bitcoin remain "dirty" and subject to confiscation as proceeds from illegal conduct? I don't really want to be a test case for that.

How does deliberately mixing your coins with the proceeds of illegal conduct help that situation at all? I don't think the government will consider mixing to be a magical crime eraser. Mixers will be the test case.