You're again conveniently forgetting the phone swapping arguments. Not all SIM swapping is about changing carriers and changing the SIM in a phone. It might be about switching the phone you use your SIM in to.
The fact is, this gives control to Apple, it gives control to the carriers that oversee the provisioning systems, but it sure as heck takes a lot of control away from consumers for ... what benefits exactly ?
There are too many questions unanswered to blindly call this a good move. There are a lot of lost benefits however that warrant questioning this.
I don't know anyone who has ever switched their SIM from phone to phone the way you describe, which is interesting because you seem to be claiming it's an important feature that everyone uses (judging by your tone).
I don't doubt someone somewhere does it, but it certainly isn't a matter of course for many very good reasons. One of them being that switching the SIM doesn't carry over all, or even most of or much of, your data. Far less than half of my contacts and other data are stored on my SIM. If my phone crapped out or the battery ran out and I had an emergency that required me to use a phone, I'd... use the phone in my office. Or a phone of someone I was with. Everyone I know has, essentially, unlimited voice these days. Even if it's not actually unlimited, they use it so little that they're never close to running out. Nobody cares if I use one of their minutes for some emergency (which has happened one time in the last ten years).
I also find this argument ridiculous: "But switching with a built-in SIM will make you vulnerable to carrier fees!" News flash: carriers already track which phone your SIM is in, and if they want to charge a fee to let you switch it they will (some do in the U.S., though thankfully less as time goes on). In places where such fees are already outlawed, they still will be, and in other places, like the U.S., there is, and will continue to be, pressure away from not toward these fees.
I just don't see that SIM-switching has any real benefit (as noted by someone else, it makes roaming in Europe a PITA because you have to have the different SIMS around and hope you don't lose them), and it has some definite drawbacks from both the consumer side--having to worry about the different SIMS for traveling--and the handset-maker side--increased design complexity, cost, and fragility.
