Imagine that I own a spacecraft with a Star-Trek-style teleporter. I roam the galaxy, stopping off to beam down and visit the many planets of the human diaspora, sometimes beaming up guests to visit me on my ship. One day, I am enjoying a game of droneball in the teleporter room, when I accidentally hit the ball onto the control panel, smashing the keys and setting off the teleporter. I hear that familiar noise and see a flash of light, and a woman appears in the teleport zone.

I have no idea where she came from. My long-range teleporter (which is now broken) could have beamed her from anywhere. She is babbling in some foreign language that I don’t understand, so at least for the moment she can’t tell me anything useful. It might take me months to track down her homeworld or find a spaceport that will accept her. In the meantime, I will have to feed her and give her lodgings on the ship, which is all going to cost me. She might even be dangerous or pose some risk to my health.

I don’t want this woman on my ship. What should I do? I reflect for a while and consider some arguments.

Firstly, I never intended to teleport anyone onto my ship, it was just a regrettable droneball accident. This is my ship, my property, and she was not invited. I have a right to choose who gets to stay on my ship, and I never chose her. Doesn’t that make her a trespasser? Having someone else onboard is going to cause major problems, disrupt all my plans, and might even be dangerous. Isn’t it my right, as the owner of the ship, to evict anyone from my property whom I didn’t invite? I can simply open an airlock and eject her into space.

On the other hand, it was my fault that she got teleported here, even though I never meant to do it. She never had any say in the matter and is innocent of any role in this mess. I know that if I eject her into space, she will promptly die. Do I have the right to take her life? After all, I do have an alternative to killing her: I can put up with her until I’m eventually able to drop her at a spaceport. I know that I’m not positively obliged to care for any random stranger, but doesn’t the fact that I put this stranger in danger give me responsibility to get her out of danger?

Let’s assume that I accept the non-aggression principle and I want to act ethically. If I teleport someone onto my ship by mistake, is it an act of aggression to force them off into space (and certain death)? Or is it an act of self-defence of my rightful property (my ship)? What if somebody else had teleported the woman onto my ship without my consent? Would it then be an act of aggression for me to eject her into space?

Whatever your answers to these questions, the same logic applies to the following question: does abortion violate the non-aggression principle?