Yeah, as someone who works in healthcare IT, what we call "insurance" in the US for healthcare in no way resembles a proper insurance model. It's heavily slanted in favor of the insurer, who have zero hesitation kicking people out of the pool, despite having accounted for their costs in their actuarial tables. Despite the fact that the risk of having condition X in the population doesn't change, you're subject to limitations and/or outright rejection should you choose to use that free market you seem so fond of. You can equally be kicked out of that pool despite having made that sacrifice you describe.
For example, health insurers have been found to have done such things as kick cancer patients off insurance as a pre-existing condition, based on previous general practitioner visits. "Oh, we, and you, didn't know it was cancer at the time, you were just sick. But since you were sick shortly after getting insurance, you most likely already had cancer. Therefore it was a pre-existing condition, you didn't disclose it, whether or not you knew about it, and we are terminating your coverage back to the first physician visit about your illness".
Or "We are refusing to cover the costs of the ambulance/air ambulance ride that ferried you to the trauma center after your MVA, because that ride wasn't pre-approved by a call to the insurer".
Both of the above examples happened. I'm not sure what should have happened in either case, but I'm pretty sure in the latter it wasn't, "Hello, Blue Cross? This is John, I'm a paramedic working on one of your patients who was hit by a truck. We would like to fly him to the hospital due to his extensive multisystem trauma but we need your approval. His name? Hang on, let me find his wallet. No, that's Smythe, S-M-Y-T-H-E, sorry, it's a bit loud with the jaws of life in the background... Yes, I can hold for a nurse consult..."
Health insurance in the US is amortization of costs, and has little to do with risk pooling and actuarials.
For example, health insurers have been found to have done such things as kick cancer patients off insurance as a pre-existing condition, based on previous general practitioner visits. "Oh, we, and you, didn't know it was cancer at the time, you were just sick. But since you were sick shortly after getting insurance, you most likely already had cancer. Therefore it was a pre-existing condition, you didn't disclose it, whether or not you knew about it, and we are terminating your coverage back to the first physician visit about your illness".
Or "We are refusing to cover the costs of the ambulance/air ambulance ride that ferried you to the trauma center after your MVA, because that ride wasn't pre-approved by a call to the insurer".
Both of the above examples happened. I'm not sure what should have happened in either case, but I'm pretty sure in the latter it wasn't, "Hello, Blue Cross? This is John, I'm a paramedic working on one of your patients who was hit by a truck. We would like to fly him to the hospital due to his extensive multisystem trauma but we need your approval. His name? Hang on, let me find his wallet. No, that's Smythe, S-M-Y-T-H-E, sorry, it's a bit loud with the jaws of life in the background... Yes, I can hold for a nurse consult..."
Health insurance in the US is amortization of costs, and has little to do with risk pooling and actuarials.