For years, ObamaCare critics focused on its least popular feature — the mandate that everyone buy insurance — taking their fight all the way to the Supreme Court.

But as ObamaCare's official launch date approaches, even its backers are beginning to admit that the law could actually create powerful incentives for millions of people and thousands of businesses to drop their coverage, despite the mandate.

There is growing concern, for example, that the law's market reforms will cause a huge "rate shock," particularly for those young and healthy.