You're right, of course, you can have SSO without the ID scheme. But even those have an identity provider, which will be subject to government requests to allow access to consolidated information about people. Better not to have that all together in one place.

And what concerns me is that one of the specious reasons the government gives for bringing in this system is that SSO makes life so much simpler, that we'd be mad not to embrace it. And for most people, SSO probably does sound beneficial; that's why I wanted to emphasise - somewhat sensationally - the problems. Shocking, I know.