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.
For the sake of argument, let's say I accept your last statement as true. Seems to be small beer, the difference between both views prosecuting assault, while one side believes that political violence is especially damaging to our liberties. Where does the obsession and venom that you have for libertarians come from? Has to be more than this.