You can generally switch if you have a supplement and move from one state to another. You can do a try-it with Medicare Advantage either when you first enroll or later if you have an existing supplement plan for a year and switch back. In many states companies are required to charge based on medical underwriting. I'm actually only specifically aware of one state which allows a later switch, and it requires enrolling in a specific Medicare Advantage plan when you first enroll.
So, for most people, it is a once in a lifetime choice - and ought to be made with the same gravity that any other once-in-a-lifetime choice is made. Far too many people are unaware of this until it is too late.
The point of the medical underwriting is to keep the costs down - to avoid people buying in only once their personal costs become too high to sustain. Ultimately, a supplement plan is still an insurance plan - and if people are allowed to buy in only when they need it, the plan will be unaffordable. That is true whether there is a public option or not. A public option will be just as unaffordable if people are permitted to buy in only once their medical costs become unsustainable - because the price will be not just age-based, but also based on the medical conditions of those who choose to buy in. So if only sick people buy in, the price goes up.
I agree the system would work better without an insurance middleman, but to keep it affordable it would still need similar restrictions (or penalties) based on late buy-ins.
And, it goes without saying, we could avoid all of this if we had universal health care.
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