Also imagine that we agree that one way to verify whether something would be bad is to try it on oneself (or imagine trying): if something is bad when done to me, it is also bad when done to someone else. The reason is that bad is bad, and good is good. Unless there is a particularly compelling reason why another person should be different from me, I must assume that if action X is bad when I am its target, it must also be bad when another person (no different from me in any important way) is its target. For instance, if killing me is evil, then killing someone else is equally evil. (I realize this is rather simplistic, but we are starting from very general premises. I.e., hold yer herses!)
But then there is a problem of diffuseness of human nature. All people are different. I may not like to receive pain, but a masochist might. I may like to eat fish, but my wife doesn't. Therefore, I must generalize the sort of things that I would not like done to myself and therefore should not be done to others.
It seems to me that respecting my wishes about what I may do in my life is one such way to generalize. There is no reason for a sadist not to apply pain to a masochist if such an application is consensual. But what about the Golden Rule: surely the sadist would not like to experience such pain? Yes, but the masochist doesn't mind. So, if the sadist can imagine that it would not be evil if something was done to him that he didn't mind, then he must realize that doing the same to someone else is also not evil.
The same goes for the masochist: he works as a hairdresser, and the sadist asks to give him a buzz cut. The masochist would rather die than get a buzz cut himself (he cares about his long ponytail very much). How can he reconcile his views of morality with the sadist's request? Similarly, he must abstract the sadist's request to "doing whatever he desires", not to the particular content of desire in order to discover that it is not evil to do so.
This approach seems to arrive at the libertarian non-aggression principle: that the basics of morality (at least in interpersonal relations) is respecting others' freedom and not coercing them to do anything against their will.
* * *
A situation may arise when two wills are in conflict. What is the right thing to do then (either for one of the wills' holders or for a third party)? Somehow we need to assign primacy to the wills. We have no choice at this matter, because A wants to do something with object X, and B wants to do something else with the same object (or wants something done with it, including leaving the object alone).
We cannot do nothing, because that would be worse. I.e., we have the following choices:
1) Honor A's wishes, but violate B's;
2) Honor B's wishes, but violate A's;
3) Violate both their wishes (which is doing nothing).
Clearly, third choice is the worst of all evils. We must choose the best.
This is where property rights come in. Property rights are ways for resolving the conflict between A and B by assigning primacy to one of their wills. I think if we knew that A expressed his will regarding X first, that would give a greater legitimacy to his claim. For example, if a cannibal wants to eat me, and I want to continue living, I have primacy to my claim, because my occupation of my body was there first. Likewise, if someone wants to use a stick that I found, I have a right to refuse him, since my will over the use of the stick takes precedence.
But, I cannot formulate this intuitively self-evident concept very clearly. Also, I cannot formulate why someone should get the right to control his money over a person who needs that money to survive. Note that I don't care about the government here. I mean what is fair and moral: if someone takes someone else's money by force because he needs it for medicine, should we let him keep it? Should he not have a moral problem himself stealing it, since he needs it more? I.e., why should we assign primacy of will based on homesteading rather urgency of use (determined in whatever way, possibly by a third party) or some societal purpose?
Some people may argue that this is a rather arbitrary way of determining the primacy of use. Who gets to be the judge? I am not convinced this is a good argument. First of all, a person may ask someone who he thinks is impartial to judge what is more urgent: e.g., to send one's kids to yeshiva or to pay off mortgage. Second, we will need to use third-party expertise to judge the evidence over first-come use (homesteading) as well. I need to have some evidence as to whether I used something first.
Admittedly, such evidence can be much clearer than arbitrary judgement of urgency. So, perhaps this is the answer: dividing property up based on who took possession first is less arbitrary than dividing property up based on urgency of use. After all, how do you determine what's more important: to send kids to yeshiva or to pay off mortgage?
But a bleeding-heart liberal (or libertarian) may argue that in all such dubious cases, rely on homesteading, but in the case of life-and-death (or health) vs. luxury, give precedence to that which maintains life...