The main reason that most universal health care systems require an individual to have insurance is so that you can't suddenly buy coverage when you become sick, then opt out when you no longer want to pay into the system.

This is no different from any other basic public service. You can't opt out of paying for schools once you graduate, or for police departments when you're not in danger, or for local roads when you're on a vacation. Even if you're not personally in need at the moment, someone else is. The only way to be sure that those services will be there when you're the one in danger, is by requiring everyone to help support the service.

I do not think that the ACA's individual mandate remotely violates any rights; in fact, since the fee is relatively easy to avoid, it's less intrusive than even an ordinary tax.

Edit: a lot of people are pointing out that the mandate is different in that it requires to to buy a private product. I would counter this by saying that the tax isn't for the insurance itself, but for the government's guarantee that you will not be turned down due to pre-existing conditions or poverty.