Honestly, your first sentence doesn't make sense to me and I've read it a few times. Those countries aren't filled with idiots. They have budget offices and can calculate the cost of the medical care in their countries. Beyond that, I'm not sure what you're saying.
"Doctors would never take just Medicare rates." Honestly, in most cases they wouldn't have a choice. Doctors aren't exempt from market forces. What's the alternative? Take what the single payer is willing to pay or make no money? What would you do? Doctors have made what they have made because individuals are divorced from the cost of their medical care. 99% of the country could not pay the current high cost of medical care out of pocket. That would continue to be the case. How many Doctors would be able to tell patients "That broken arm is going to cost $20k and BTW I don't accept single-payer" ?
"Oh and what rewards are there for being healthy? Everyone pays the same regardless. Dangerous combination with an already unhealthy country." This literally made me laugh. Americans? Healthy? That's a funny one. The incentives under the current system obviously aren't working. It's hard to imagine this would get worse because you implemented a single-payer system.
"People’s lifestyles are what makes care so expensive in this country." One factor certainly. But inefficiencies, people not getting preventative care, tort, ... There are a ton of things that make medical care unnecessarily expensive here.