I know Americans and Britains will shoot me for this suggestion, but I
am of th opinion that digital signature infrastructures are the job of
the government, just as passports and drivers licenses.
The US government is not trustworthy. A government that will break its
own constitution at a whim will think nothing of issuing false credentials,
revoking certificates, and committing identity theft any time it is
convenient (of course they will claim it is in the national interest but
nobody will be able to verify such claims); and a government-controlled PKI
would give them much more ability to do this than they currently have with
paper documents.