Insurers don't want destruction of the employer based model because then they have a middleman with deep pockets, and aren't directly responsible to you. They also have the unfathomable protections of ERISA that allow them to mess with you with IMPUNITY (while you don't get to shop around) - That's how they deny care and cancel coverage even while you are with the same employer but expensively sick. There is an entire employee benfits industry which of course doesn't want this system wrecked.
The Democrats behind Obama are not being candid about this. They have already made the Devils' deal in an attempt to get support from those industries.
With a public option safety net for those people who run afoul of the employer-based coverage, those insurers would then be faced with recovery experts from the government to enforce their requirements, instead of leaving a sick person in financial crisis to do the fighting. That's even without destrying the employment-based status quo. If you destroy that as well with people having a myriad of DIRECT purchase options AND a public ption to choose from, we would have very serious reform.