The reason was to draw attention to what they felt were similarly unfair and unconstitutional requirements in "ObamaCare" to purchase health insurance.
On a lark, I looked at another requirement that SD has: car insurance.
"If you drive without liability insurance, you could be found guilty of a class B misdemeanor. You could face a fine of at least $150. If you are involved in an accident you will be assessed 14 points against your driver's license, which will cause an immediate suspension of your license. If you don't maintain proof of financial responsibility, your license will be suspended for anywhere from 30 days to one year. You could also face 30 days in jail and/or a $100 fine. Plus, you'll have to show proof of insurance through a SR-22 filing with the state for three years from the date that you were found guilty. The SR-22 form is proof that you have insurance on all the vehicles you own. Even if you don't own a vehicle, you'll still need to have an operator or non-owner insurance policy.
$25,000 for injury/death to one person
$50,000 for injury to more than one person
$25,000 for damage to property
I thought that was interesting. You have to maintain proof of financial responsibility when it comes to driving, but not for health. I really liked the last line there, "Even if you don't own a vehicle, you'll still need to have an operator or non-owner insurance policy."
New Hampshire, on the other hand, does not require any type of insurance to operate a vehicle on public roads.