For example, you go into the hospital for abdominal pain, but it turns out that you need a massive orthopedic surgery to fix a congenital issue that only 2 surgeons in your area can perform (true story). Or you are a severe diabetes or lupus sufferer who has routine hospitalizations for a variety of infections you get at random due to their underlying condition. Need a tooth filling replaced? Of course, shop around. Need emergency dental surgery because you had traumatic facial impact playing soccer? Not so much. Emergency treatments to sick geriatric patients to extend their lives by weeks and months: also very expensive.
Routine doctor's office visits to remove a wart from your foot, or diagnose a sore throat, which you can shop around for, are not where the high costs comes from.
Yet those do have insanely high costs as well, as compared to the rest of the economy. We live in an economy where medicine tends to get more expensive, rather than less, i.e: https://www.nbcnews.com/health/diabetes/u-s-insulin-costs-pa....
Doesn't it make sense to figure out why the basics are getting more expensive, before suggesting we engage in a national price-fixing experiment?
Giving everyone their own money for, say healthcare costs, and having them navigate markets alone... achieves exactly the kind of divide-and-conquer that price-gouging pharmaceutical companies and hospitals have wet dreams about.
The only good UBI supplements, but does not replace, most existing social welfare programs.
Replacing existing programs just creates an open season for vultures.