Selling across state lines doesn't help anyone if you are also mandated to sell an identical product at the same margin.

One of the reasons premiums were going up is that states were using insurance mandates for political gain, pandering to interest groups. Requiring providers to cover things that most people would prefer not covered in return for a lower price (ie. fertility treatment, substance abuse treatment, sex changes, etc.).

If someone has a legitimate claim that is denied by the insurance companies, that is illegal. It's a law enforcement issue rather than a health care one. Don't confuse legitimate claims with types of coverage. There are lots of people that would rather pay a lower price for health care if they can rule out certain coverage for themselves like sex change operations.

Government mandated coverages is like forcing people that don't live near water threats to pay for flood insurance or making a person pay for business liability insurance just in case they someday start a business.