Saw it coming and frankly think it's almost the best reason to be opposed.
The other contender for #1 is that this bill hands the job to the very same insurance companies that cause the high costs.
Let's face it, if you went into a shop to have your car fixed, and they gave you no price estimate upfront other than "possibly unlimited" - would you go to that shop?
If you saw what those MRI's etc were really being billed at, and had to pay yourself, would hospitals have 3-4 machines apiece mostly sitting unused? No, they'd maybe have one, mostly unused. Or would you willingly ask for sweeping batteries of tests that cost you $100 each for 25 cents worth of chemistry? Hell no, you'd look for a more competitive price on this stuff. But since insurance A: doesn't show you the real bill - or at least you don't have to pay it directly, you don't care - if it was coming straight out of your pocket, you, like them, would demand lower prices. But the insurance companies don't even pay that much - they get negotiated price reductions on the order of 40% - and don't want more because guess what - the state guarantees them "cost plus fixed fee" when it's rate regulation time - so they want high costs as this boosts their fixed percentage of costs profits.
I know this due to another cool story I gotta write up for here about my little experience uninsured in the hospital after a high power rifle bullet tore off one side of my face and head...the billing was amazing (ly bad), and I actually got the hospital agent to admit that no insurance company would have paid that at face value, and told me the number. I did (much) better, but that's part of the cool story.