That's what I find most wild about this argument. Not only is insurance paying for other people's healthcare, you're also paying to enrich a bunch of shareholders.
Profits in the healthcare industry account for a single digit percentage of costs. Health insurers made $35 billion in profits in 2019: https://www.fiercehealthcare.com/payer/big-name-payers-earne.... Americans spent $3.8 trillion on healthcare that year. Okay, get rid of insurer profits. Your costs have gone down less than 1%.
With single payer healthcare, that money goes to the government, which is bad.
In the current US system, that money goes to private companies, which is good.
Don't bother questioning this because it's axiomatic. It has ceased to be merely political theory; it's now core to many people's identity. Any threat to that status quo is a personal, existential threat.