Medical care is not unequivocally a private good.
Near as I can tell, the OP wasn't talking about it either.
By way logic does a libertarian say that e.g. government coercing people to obey quarantines is acceptable, but that the government coercing people to pay for cheap public preventive care (before expensive specialist treatments become necessary) is not?
For comparison, compare laws against punching other people to laws against punching yourself.