Legal scholar Richard Epstein has a long, carefully detailed article at explaining why the Reid bill fails to pass constitutional muster. From his introduction:

In effect, the onerous obligations under the Reid Bill would convert private health insurance companies into virtual public utilities. This action is not only a source of real anxiety but also a decision of constitutional proportions, for it systematically strips the regulated health-insurance issuers of their constitutional entitlement to earn a reasonable rate of return on the massive amounts of capital that they have already invested in building out their businesses.

Read the whole thing here. Read Epstein's Reason archive here.