This is one of, if not the, dumbest argument I ever heard in my life.
Let us look at the facts:
Bitcoin market cap...about $100B
Bernie Madoff scam..roughly $60B in USD.
One ponzi scheme is about 60% of the entire value of bitcoin.
And we arent even going into the bankster led mortgage back security scam that costs institutions and people trillions.
But yeah, let's focus upon the few isolated areas where bitcoin is used for illegal activities.
Smokes screens, idiots shouting and other idiots listening to them. I think that sums up the problem