Re: Worst argument ever
"Is it not the case that though it is much harder to buy 'illegal' stuff with money"
Nope. In the exact same way that legal transactions can be settled with cash, same applies for illegal ones. I very much doubt the street dealers around here will accept a crypto transaction, I'm reliably informed that they do take euros, dollars and even pounds.
"It is generally more difficult to get hold of illegal stuff with cash as you have to actually hand it over in person to receive the goods I don't think that major drug purchases are done by post - for a start, the postal cost for a briefcase of money would be pretty high! whereas crypto is just a click of a mouse with zero traceability."
With the exception of deliberately obscured crypto currencies (eg Monero) crypto is considerably more traceable than fiat. You can do it without needing any special technology or legal recourse, wheras most bank details will require some level of justification from the appropriate authorities, and are not available to the general public.
In fact letters and parcels are about as easy to track too, which is how those drugs-by-post dealers get busted. They are not getting busted by tracking their transactions. That comes later, when you've been convicted, and the government says "please provide evidence that these assets have been legally acquired" and seizes everything that you don't provide evidence for.
"So whilst, not an amazing argument, it is not the 'worst argument ever'"
It's a crap argument. A guy with billions of dollars insists other currencies are used for bad things, but their own currency is only used for love and happiness.
I put it to you that more people have dies of opiate overdoses in the USA that where purchased with USD than people who have dies from purchasing it with crypto. People have been buying opiates with USD for several hundred years, as compared to ~10 with crypto. Thus for crypto deaths to have been even equal, they would need to cover 93% of sales of opiates.