As I understand your point it has absolutely nothing to do with it being illegal to not have a SIM card. Your point is simply that it is impractical not to have a SIM card because that makes it difficult to do bank transactions. Big difference, and using 'illegal' in this context is highly misleading.

I think the implication is that if you wanted to function without a SIM card, your only way to do that would involve eschewing all above-board fiscal infrastructure and working with the grey/black market instead.

It's like being an outlaw, or a member of an untouchable caste: sure, you could just hide in a hole forever and wouldn't be breaking any laws, but in order to do anything you'd have to do it in a way that breaks a law.

But that’s just not true.

My point was really that the banks will be forced (by EU)to drop sms as SCA anyway. Legislation for that to happen is already in place.