In practice what is "legal" is whatever the State says is legal, as they have the guns to make people jump.
Some basic assumptions that I've been keeping lately:
0. Rights are nothing more than agreements between human beings.
1. Might wins the right.
2. All human beings act on self-interest.
3. Each individual's self-interest is subject to individual preferences and circumstances, so
all value is subjective to individual preferences and circumstances.
4. If one wishes to live in a society in which nearly all human beings achieve the maximum level of self-interest/satisfaction nearly all of the time, the dominant culture of that society must abolish the initiation of threats and acts of bodily harm against any individual, and the taking and/or breaking of his stuff without his consent.
The State is a group of people that primarily initiate threats and acts of bodily harm in order to get everybody else to pay them money so that they can fulfill their personal self-interest. They get away with this by bribing various other groups of individuals with various promises of fulfillment of their own self-interest; though quite often the mightiest are the only ones that actually see such promises kept. Dominating cultures throughout the world tolerate such an organization for the same reason people play the lottery: while 99.999999999999% keep losing, or get some pocket change from it, they keep on playing the game hoping that they might actually win the big one, never mind any injuries caused to others in the process.
( from an email conversation I've been having with a friend )