It is fine by my standards to use force to respond to force initiated by another individial.
It must be directed only at that individual.
So speed limits should only apply to people that have actually run into you? Fascinationg.
How about my second point? I call this the "Gunga Diner" example. We all know that medical schools give money to winos to have them sign a release stating that after they die, the med schools can use their cadavers for medical training. Right? Ok, now your standard for what government can and cannot do is the "non-initiation of force", right? And you support the right to freely contract, as long as a person is at an "age of reason", right?
So, what if there's a group of people that wants to eat humans after they die a natural death? Let's say I start a restaurant--the Gunga Diner--that voluntarily contracts with terminally ill people to sell their bodies (for--I don't know, $500 a pop?) for food after they die. Ok? Now, you as a libertarian should have no problem with this, right? No violence was initiated against the people agreeing (they weren't killed; they died of natural causes), and they freely contracted of their own free will. Why is this not okay? Or is it? Even more disgusting example--why shouldn't parents have the right to sell their deceased children to said diner? Their children are their "property", aren't they?
I hate to be so disgusting, but sometimes it's necessary.