Libertarian Philosophy is based on the idea of opposing aggression, whether open violence or under-handed fraud. A libertarian society would be much tougher on violence than our society, where some violence is ignored because it serves the purpose of some people in power or why has Jesse Jackson never been indicted for extortion?
Secondly, one Libertarian does not equal Libertarian Philosophy. Again, I ask why you are obsessed by libertarians? They're the big threat today?
There are already laws against assault. The article posits the idea that violence motivated by politics causes far worse damage to our liberties, and it is that very idea where the libertarian ideology falls far short in being able to address.