Help to reconcile individual rights and criminal charges as a result of causing another's death unintentionally due to their own failure to take safety precautions, as would be their right.
If you instigated the crash that killed someone in another car who was not wearing their seatbelt (this is your question, right?) then you are at fault. Their lack of a safety harness certainly contributed to their death in the grand scheme of things, but not when it comes to the justice of the situation. A counter scenerio: Several people are at the firing range. The range is declared to be cold (ie. no shooting). One shooter is not paying attention and through a negligent discharge kills another man walking down range to collect his target. Is he not at fault because the victim failed to wear a bulletproof vest? Absolutely not.
Those who advocate for the government will argue that certainly more deaths will occur if there is no law that one must wear a seatbelt. Further, they say a law for wearing a seatbelt will be in everyone's best interest since it may protect someone from dying, in the even that you crash into them, thereby preventing you from being charged with vehicular manslaughter.
It is hard to argue (with a friend of mine in this case) that when one decides to drive one should assume the risk of potentially killing someone due to another person not wearing a seatbelt since certainly the chances are greater (without a law) that you could kill someone. They argue that if there had just been a law, the chances of death and of you getting charged with manslaughter would be less. A win-win. (of course we all know this is actually a Win-Win-Lose since it comes at the expense of the people due to requisite taxation to enforce a seatbelt policy)
On a slightly separate side of this:
Could we reply by saying that a privatetly owned road could enact similar rules as would be the case for a government to implement (if they found that it did indeed benefit consumer confidence and demand for usage of the road) and by doing so could we avoid delegating responsibility to the government to "care for our safety"? Essentially, transferring the interest of the rule from that of government watching over us, to a private enterprise doing what is in their best interest to guarantee ultimate profitability as an economic solution to avoid giving power to the government...?
Also, with such a government law of wearing a seatbelt comes our current day police system. AT LEAST ( if not for impacting safety in any way ) privitization of roads would make policing more efficient so that we will not get taxed for government inefficiently enforcing seatbelt regulations...?
You don't assume the legal risk of potentially killing some just because they don't wear a seatbelt though. In order for it to be considered manslaughter, there has to be some hint of recklessness or negligence on the part of the offending driver. If the goal is to reduce the risk of manslaughter, then the most effective laws would be those that reduce reckless or negligent driving (speed limits, no texting laws, etc.). Of course, the costs of those laws are generally much higher than their benefits.
they said we would have an unfair fun advantage
http://www.libertariannews.org/2010/02/27/seatbelts-cause-more-pedestrian-and-cyclist-deaths/
This might be of some help to you.
Sealt belts are safety harness designed to secure the occupant of a vehicle against harmful movement that may result during a collision or a sudden stop. Between May 21 and June 3, 2012, Michigan police seat belt crackdown gets results. Over 8,000 tickets were printed, more than 1,000 above last year's total. Will you be looking to purchase or sell a used or new auto?