One would assume that libertarians and free marketeers would cheer the concept of boycotts, as it is one of the mechanisms that citizens are empowered with in a laissez-faire society.
Why not pass such a law? Because that would effectively mean semi-nationalizing a fairly large industry, and if we're going to do that, why not just create an actual single payer and a risk pool the size of the US population and skip the idea of having private firms involved at all.
The biggest problem with the idea of single payer "insurance" is that it's not actually insurance. It bundles in a variety of things such as pre-payment for services, wealth redistribution, price controls for services, and some actual insurance.
A social safety net is a good thing. But if we expect to benefit from the benefits of a competitive system, we have to let firms actually compete.
The core issues have to do with the lack of "insurance" market for things that are actually prepayment (like giving birth, dying of old age after $50K worth of end of life care, etc).
By mandating that consumers buy the "insurance" and mandating that insurers bundle all the non-insurance services into the package, the government essentially controls the market and avoids both the benefits of market competition and accountability for tough decisions such as which care should be covered, etc.
There have been many threats from industry and government. Government can nationalize and can pass laws that reduce profits, and firms can pull back, can merge with each other, and do other things to increase their market power.
The bottom line is that the entire system is ripe for corruption and lack of accountability. Let's face it, for a healthy young person, catastrophic insurance is next to free. Yet all of us are paying fairly high premiums so that old people can be exploited by a healthcare system that happily gives them ineffective surgeries and sells them overpriced and largely ineffective pharmaceuticals.
The system was already corrupt before Obamacare, Obamacare simply cemented many of the most lucrative public/private deals. Both sides intended to scheme a bit after the programs got underway. So we'll see a bit of tit for tat with regulators and perhaps watch one or two of the entrants leave the market allowing the profits to be divided fewer ways.