I'm skeptical that the health problems created by a largely obese population will be so expensive that they will destroy a universal healthcare program.

42.4% of adult Americans are obese, and yet obesity related healthcare costs only cost the US healthcare system $173 billion per year. That may seem like a lot, but considering that the total cost of the US healthcare system was $4.1 trillion in 2020, it's only about 4% of the total healthcare budget. Weather or not public healthcare can succeed will not ultimately depend on the obesity of the population.

DISCLAIMER: All of the statistic in this post are just the from first results that popped up while Googling, so these statistics are certainly flawed. For instance, why did I use 2020's healthcare statistics? That was would almost certainly be an exceptional year for healthcare spending. Also, I'm suspicious of the 42.4% Americans obesity statistic. Maybe I just live in an exceptionally healthy part of the country, but I don't think I see that many fat people in my day-to-day life. However, I'm not going to look to deeply into it, because I'm not interested in truth, I am only interested in justifying my gut reaction.