1) since the exchanges can't discriminate on pre-existing conditions, many people with expensive pre-existing conditions in need of treatment will sign up.

2) because a high percentage of the new customers to the new plans need expensive treatments, insurance companies are forced to raise the rates on the new plans to cover costs

3) after seeing the higher insurance rates, healthy people quit the plan since their expected healthcare costs are lower

4) repeat steps 2 and 3 until very few people can both afford to be in the plan and have very pressing healthcare needs.