You can't just say depositing money on a site is a crime, there were plenty of non-illegal things bought and sold at the Silk Road. Plus evidence of intending to one day maybe buy something illegal is not evidence of having bought something illegal.

Tangentially related, in the cases where the USG seized offshore gambling sites, they returned deposits to the players, even though playing there was ostensibly illegal.

Granted offshore gambling is a little murkier than buying heroin in terms of legality, but see paragraph #1. Having funds at/on TSR is not a crime.