If you were born with Asperger syndrome, should people be forced to date you? Most of you would probably say "no." It's a good answer: why should people be punished for something that isn't their fault? So why do so many believe health insurance companies should be required to accept applicants with pre-existing conditions? (Before you respond with "I don't want to date someone who doesn't want to date me," remember Asperger syndrome severely limits your ability to read social cues; you won't be able to tell they are with you only by force.)
It's not even that insurance companies won't cover pre-existing conditions. It's that they won't cover them at a particular price: a low price. In the end there are those randomly burdened with a condition that's expensive to care for and they don't want to pay for it (at least all of it). But that does not translate into forcing someone else to cover the costs.
And no, insurance companies are not sitting on lots of excess cash. Record profits are not the same thing as high profits (and even if they were, proposing a permanent change based on temporary conditions is very reckless way to make policy). Because they are barely profitable, forcing their costs up with such reforms will force prices up and making it too expensive for someone who could otherwise get it. Now we are forcing our neighbor to carry the burden of our condition. Where's the justice in that?