For instance, in the case of lifesaving treatments, the demand is essentially infinite, and this is a fact which Pharmaceutical companies use to raise the cost of treatment to astronomical levels. When the alternative to expensive treatment is death, there is simply no countervailing market force to bring costs down.
The same goes for pre-existing conditions. It may have been fine for you and your wife to pay for a reasonably-priced high deductible plan, but without the ACA, that simply would not be an option for a huge number of people. Without government regulation, there is absolutely no incentive for an insurance company to cover a chronically ill or high-risk individual. The rational way to operate that type of business in order to maximize profit would be to cover healthy people only, and remove anyone from your coverage who is likely to file a large claim, and we have seen this come to pass.