Objectivist philosopher Leonard Peikoff has argued that a fetus has no right to life inside the womb because it is not an "independently existing, biologically formed organism, let alone a person." Pro-choice libertarian Murray Rothbard held the same stance, maintaining that abortion is justified at any time during pregnancy if the fetus is no longer welcome inside its mother. Similarly, other pro-choice supporters base their argument on criminal trespass. In that case, they claim that the NAP is not violated when the fetus is forcibly removed, with deadly force if need be, from the mother's body, just as the NAP is not violated when an owner removes from the owner's property an unwanted visitor who is not willing to leave voluntarily. Libertarian theorist Walter Block follows this line of argument with his theory of evictionism, but he makes a distinction between evicting the fetus prematurely so that it dies and actively killing it. On the other hand, the theory of departurism permits only the non-lethal eviction of the trespassing fetus during a normal pregnancy.