And just what percentage of your income goes toward healthcare right now -- both for you and for other people?
My wife and I pay $600 per month in post-tax dollars for our health insurance, thanks to Massachusetts' healthcare plan which lets anybody buy group insurance through the state. (If it wasn't for Massachusetts, I'm not sure what we'd be doing for healthcare -- we're both independent contractors, and you can't buy health insurance through IEEE anymore -- so I consider myself lucky to get that rate. And if that sounds incredibly expensive to you -- well, congratulations on being 23 years old! But don't expect to be 23 forever!!)
The median annual household income in Massachusetts is 60K. (Source: http://projects.washingtonpost.com/elections/keyraces/census... ). That's in the 25% federal tax bracket. (http://www.moneychimp.com/features/tax_brackets.htm ) State income tax here is 5%. So $600 per month post-tax is $857 per month pretax. Thus, the median couple in Massachusetts can expect to pay $10,285 per year for their own health insurance, or about 17% of the median annual income.
Now, you could argue that your median couple might be getting their insurance "free" from their employer. In increasingly many cases this is not true -- fewer and fewer employers provide health insurance -- but even if it is true it merely raises the couple's real income to $70,285 -- of which 14.6% goes toward health care.
Now, that doesn't count the percentage of their federal taxes that goes towards health care for themselves and other people. As a quick estimate, a handy website (http://www.nationalpriorities.org/taxday2008 ) tells me that 22% of each Massachusetts resident's tax dollar went toward health in 2006. 60K * 30% * 22% is $3960, so that's another 6.6% of pretax income toward health care.
Thus, health care costs consume something between 20% and 24% of the median family income in MA. So, if you ask the median Massachusetts resident if they're willing to have taxes raised "10-20%" in exchange for free, guaranteed, universal healthcare the first-order answer is "hell, yes" -- even if you assume that the U.S. healthcare system would remain terribly inefficient relative to other systems worldwide. Which I would hope it wouldn't.