I fully understand that, but there are other ways to get people to get health insurance without forcing them. You can easily give people say 6 months to a year to get health insurance. If they don't, instead of making them pay a fee (which might be considered unconstitutional), you just make it basically impossible for them to re-enter the health insurance market. Make them pay everything out of pocket. Only idiots would get hurt by this.
There are plenty of idiots out there willing to gamble. Keep in mind that a significant portion of those who are uninsured are those who have decided to gamble that they are healthy enough to make not buying insurance the smart option for them.