"I think this is nonsensical" ... "Actually I have a hard time charitably following his reasoning".
Let me help you a bit by over-simplyfing the logic:
- If I state an argument to you, it can either be true, false or indeterminate. No matter what argument you make to me in that regard, you'd end up agreeing with that argument, which means that specific argument is "a priori". Moreover, you can only reach a conclusion about my argument by being you, which means you need to have control over your own thoughts to achieve that conclusion (self-ownership)
- If we define ethics as the minimal set of rules that we agree upon in order to maintain our voluntarily stable pacific relationships over time and space, the only possible way we can achieve those ethics is through an argumentative process (I invite you to think of a refutation of that statement)
- Self-ownership can't be maintained (therefore invalidating the time and space requirement) without some means (food, water, shelter, etc). Those means are scarce, and can only be used by a single person at a time. So if we define property as something that is scarce (therefore delimitable) and is being used (therefore modified and protected), private property is a necessary requirement for sustaining self-ownership.
- In conclusion: A minimal system of ethics require arguments to be produced. Arguments require self-ownership to be produced. Self-ownership require private property to be sustained. Therefore if the aim is to achieve a minimal system of ethics that allow for the stable and pacific co-existence of individuals over time and space, the agreement on private property is required -- and that itself constitutes the minimal ethical.
That said, it doesn't mean that you'll agree with anything I exposed. By not agreeing, however, you are implicitly agreeing (by stating an argument). The moment you generate an argument, by the means of logic, you're agreeing on the minimal ethics of private property (although you may not be acting in alignment with that ethics).