> The ledger as a permanent history available to the world, in real time, of every single transaction.

arguably a selling point. just not for selling large quantities of online drugs.

Or for people buying or selling anything that's currently legal but that could then become illegal during their lifetime.

Laws are generally not retroactive (though admittedly this principle does get violated).

> The Ex Post Facto Clause, contained in Article I, Section 9, Clause 3 of the Constitution, provides: “No . . . ex post facto Law shall be passed.” The phrase “ex post facto,” Latin for “after the fact,” refers to laws that apply retroactively. While the Ex Post Facto Clause on its face might appear to bar all retroactive legislation, courts have applied the Clause only to penal laws.

> Congress has much greater leeway to enact retroactive legislation in the civil sphere than in the criminal sphere. However, certain constitutional limits apply, and courts interpreting ambiguous statutes apply a general presumption against retroactivity.

https://sgp.fas.org/crs/misc/IF11293.pdf