Nitpick: you're referring to at-will employment, not right-to-work. Right-to-work laws mean that you can't be forced to pay union dues as a condition of employment. At-will employment means that you can (theoretically) be fired or quit at any time for no reason.
Though the two are related in that almost all of the employees that cannot be terminated at the employer's will are unionized. Even in the right-to-work states, almost all of the employees of governments and universities cannot be fired at will.
The worst part of it IMO is that even if you could pay for insurance without your workplace plan huge numbers of Americans can't get it at all due to pre existing conditions. So this is a serious impediment to workers leaving stable jobs that they don't like to do things like found small startups or even just move to a new job that may not be as stable.
How many Americans live in right-to-work states and can be dismissed without a reason?
Add that together and you have a lot of fear.