Not sure what you mean. Do you mean would it be ethical to kill one of them? In my opinion, once two people exist, it would be unethical to kill either of them.

Then the transporter should never destroy the source person, right? That's my whole problem with the idea. Imagine that the technology to destroy the person at the source didn't exist (this is fantasy tech for the purposes of philosophical naval-gazing, afterall), and the machine simply shot you to death after completing the upload to the source.

According to the psychological continuity theory, it shouldn't matter what happens to the original body, as long as the experience is the same. Whether your original body is vaporized or shot, you experience entering the teleporter on Earth and emerging from the teleporter on Mars a moment later. You weren't killed, you were transferred to a different body.

Of course, you don't have to agree with the premise that personal identity is psychological continuity. But I think there are other thought experiments that make the bodily continuity theory counter-intuitive. What if my brain was transplanted in such a way that I experienced going to sleep in my body and waking up in someone else's body, with my memory and personality otherwise unchanged? The bodily continuity theory says I would be a different person, but my intuition is that I would still be the same person, just with a different outward appearance.

Speaking as a potential original body, screw that - I'm not setting foot in a teleporter. But if other people want to try it, that's interesting too. Of course, it's hardly a new problem/paradox; if you haven't seen Christopher Nolan's "The Prestige", it's worth a watch and this is a plot point. And obviously the thought experiment goes back much farther. I'd hardly be surprised if some Greek dudes were arguing about it before the birth of Christ.

Yeah, I'm generally not an early adopter of technology -- I would probably let a few million people try it out before I put my own body in it. The Prestige is excellent. Christopher Nolan has a talent for taking a philosophical concept and turning it into a great action/thriller movie.