Chief Justice John Roberts applied the word "tax" to the penalty devised by the current health-care legislation in order to help explain why he felt the concept was constitutional. The penalty itself was devised by the authors of the legislation for the purpose of enforcing participation in the plan, a very critical element for keeping health-care costs down, as explained elsewhere.
Whether we call it a tax or a penalty, or both, is unimportant. It will apply only to those people who decide they don't want, or need, to afford health care insurance. It is those people, who have accidents or who fall ill, as a certain proportion are bound to, who discover they can't afford adequate care when it is needed, and so go to emergency rooms for care. And those people who did buy insurance have to pay for it.
If this sounds fair to those people who criticize the health-care penalty as just another "tax," then I hope the rest of us decide we don't have to go along with it.