The first paragraph achieves the glorious task of knocking down a strawman.
Libertarianism opposes aggression which is generally defined as initiating or threatening to initiate physical coercion.
Therefore, I can use my own judgment to know if someone is threatening me and take proactive measures without being an aggressor. I can kick someone who is in the process of punching me way before his fist reaches me.
It should also be noted that the article talks about the "rightful monopoly of force" which implies sacrifice of the taxpayers who pay not for their own protection but also for the protection "needed" by others.