What do we mean when we say "me"? A thought experiment.

Suppose someone had invented teleportation, and humans have colonized Mars. The only practical way to get to Mars is to use the teleporter. The teleporter works by recording the state of every molecule in your body, disintegrating it, and sending the information about the molecules by radio waves to Mars, where another teleporter assembles the molecules exactly as they were.

Now, your wife has traveled to mars by teleportation several times, and she tells you that it feels fine although slightly discomforting the first time through. You decide to go visit Mars, and hop onto the teleporter. After being teleported you feel some light nausea, but otherwise fine, and Mars is a wonderful sight.

But, is the person that appeared on Mars really you?

After a week of great vacationing on Mars, you decide to go home. You hop on the teleporter, but nothing happens, you are still on Mars. You ask the teleporter operator what’s wrong, and he tells you that an error led to the desintegrator malfunctioning (but the teleportation and reassembling went fine).

Where are you now?

Suppose the error with the desintegrator also caused irreversible cancer for the body not being teleported. Your double (you?) calls from Earth to tell you that he’s very sorry about the cancer, he tries to console you by saying he will try to live out his (your?) life as best he can.

Are you upset?