It’s been five years since the passage of the Affordable Care Act (Obamacare). In all that time Republicans have not produced a single, credible alternative to it that they can unite behind. Have you ever wondered why?

Here’s one reason. The minute anyone proposes an alternative vision for health reform, he will almost immediately be attacked by his ideological comrades for being insufficiently conservative.

The latest victims are Gov. Scott Walker and Sen. Marco Rubio—two Republican candidates for president who have proposed replacing the arbitrary and unfair tax subsidies in the current system with a fixed sum, health tax credit—very much like the child tax credit. For Walker, the credit would be available to people who purchase their own insurance. For Rubio, the credit would be universal, replacing even the tax subsidies that employer plans enjoy. Both proposals would make the credit refundable—people could get it even if they don’t owe any taxes.