Paul Ryan proposed a private health insurance alternative to Medicare for future retirees, liberal critics pounced. It’s another scheme to undermine health care for the elderly by “privatizing” and “voucher-izing” the program, they said.Yet, almost one third of seniors are already in private health insurance plans. They are called Medicare Part C, or Medicare Advantage, plans. And you would be hard pressed to find any Democratic office holder who wants to abolish them. The reason? Seniors choose to be in these plans because they like them better than traditional Medicare.Not only do seniors like them, but they appear to provide...