> Maybe, but what would inevitably happen is for network operators to demand that only certified devices, or maybe basebands, be allowed on their networks.

There was already a battle between AT&T and people who dared connect phones they actually owned to the phone network, and it ended well for the general public and badly for AT&T. The cell network should not get to determine what people attach to it; it should just pass data back and forth.

(In an ideal world, the cell network would have absolutely nothing to do with phone numbers, either; it would just pass data, and phonecalls would always happen over encrypted channels to your actual phone-number provider.)

> the concept of SIM cards is a net win for everyone, in my opinion

Public/private key crypto doesn't require a card that can also do other secret operations. And it doesn't require a smartcard either.