Profit margin is relatively meaningless when it comes to health insurance companies. Especially when using it as a launching point for a discussion on public vs. private. A significant share of a health insurance company's expenditures is overhead. On top of that, with proper accounting it is very easy to artificially inflate costs (which is beneficial for them, both politically and in fiscal terms). Health insurers have wide latitude in setting "expected future payouts" in its books.
As such, a much better measure of how much money they are actually making is return on equity. That is, how much money investors are receiving based on how much stock they own.
Return on equity for health care insurance: 12.8%
Return on equity for brewers: 14.6%
That is a lot closer, huh?
In fact, over the past ten years health care insurance has had the fifth best return on investment:
http://money.cnn.com/magazines/fortu...tinv/10yr.html
Slightly behind construction and different aspects of the oil industry. You know, those two industries who had huge booms between 98 and 08?