Although that simple statement is the bedrock principle of libertarianism, it is often rejected, even by self-described libertarians. Why would someone reject that principle, and what can be done about it?
There is, within each and every one of us, an innate fear of negative externalities. As hunter-gatherers, our very DNA tells us that what another person consumes threatens our survival. Since it is impossible for you and I to occupy the same physical space or consume the same resources, my very existence imposes a negative externality on you. As nature has also provided us with the reason to form teams and divide labor, however, we accept a certain level of negative externality as long as a person produces more than he or she consumes.
Beyond that is where the trouble begins.
As Ruwart describes, you probably want to use your life and property in the manner you see fit and in accordance with your moral compass, as do I. However, if either of us does so, it will impose negative externalities on the other. By focusing on those negatives and ignoring any positive externalities that may come from your utilization of resources, I can easily construct (in my mind) a need for a mechanism that will restrict you from using the resources you control even if it means that I will also be restricted from using my resources. We even have a highfalutin name for the mechanism and its users: the cult of omnipotent government.
The hallmark of a libertarian is one who ignores supposed negative externalities and, indeed, even has a propensity to reward others for positive externalities. I recently read a comment intended to be snarky but I felt absolutely boiled libertarianism to its essence: I have a porch. I like my porch. I think everyone should have their own porch. Stay off my porch.
I am constantly amazed that an average lay person could be such a control freak that they would find fault in a live-and-let-live philosophy such as that. I am constantly amazed that choices and associations made voluntarily are considered unacceptable. I am constantly amazed at the attitude that only coerced choices and associations are considered good. I am a libertarian.
But, while I am willing to live-and-let-live, accepting your negatives and rewarding your positives, you may not be. Therefore, you will impose on me the mechanism we constructed earlier. You will use whatever means are at your disposal, including violence and often with the best of intentions, to restrict me and control my property. Because I will not, I will always lose this game to you.
Libertarianism will always be subjected by statism because it is libertarian.
You who would not follow the advice of Ruwart, you who reject the aptly-described natural mechanisms in Ruwart's own Healing Our World, will subject me precisely because I am unwilling to use violence to preemptively subject you. But in doing so, you enable those who reject the idea of liberty and property altogether, and then, you have the hubris to blame me in exactly the same way you will be blamed when the house of cards constructed by the statist falls. While the cult of the omnipotent state predates your Lockean notion of limited government, leviathan is the direct and predictable result of it.
Ruwart is quite correct in noting, rather more prosaically than I, that you have to accept liberty as the whole enchilada. In doing so, you free your fellow man, even if he will not free himself or you. By accepting liberty unilaterally, without the condition of reciprocity, you are easily subjected but you deny your subjector the thing he needs most: legitimacy. His victory is exposed for what it is, Pyhrric and juvenile. Your defense, then, of your liberty and property has the legitimacy he so desperately seeks.
Following Ruwart's advice, and unilaterally accepting all of liberty, you put the statist in a no-win situation. Even though he may beat you temporarily, in the long run he will always lose. By rejecting any part of liberty, embracing half-measures and compromises, or even describing a legitimate role of government, however, you are actively participating in your own subjection and giving it legitimacy.