Wayne Hoffman argues here that insurance companies ought to be able to sell across state lines without all the horrible regulations preventing them from doing so. He marshalls a couple arguments to try to establish it would be cheaper for insurance companies and for purchasers.
But, he either misses or ignores the most salient point. If insurance companies are allowed to operate in every state, they will simply pick the state with the least regulation and move there. Credit card companies (including banks issuing credit cards) did this back when they were deregulated, and the result was an explosion of fees and charges on consumers, along with a general jacking up of the interest charged. Oh, and profits went up for the credit card companies we well.
Insurance companies don't want the federal government regulating them; look at health care, for example. They always try to kill federal legislation. They prefer state regulation because so often they exercise extensive influence on the state government and regulators. It's cheaper to buy a few state legislators than it is a slew of Washington congressmen and women.
Letting insurance companies cross state lines is a bad idea.