But if no one has the right to decide on anybody else's life, than doesn't that mean that they wouldn't have the right to decide to let every other person on Earth die because of this one man as well?

It's the lesser of two evils if you think about it, sacrifice one sheep to save the whole herd, or save one sheep and sacrifice the herd.

Also, if you want to get completely philosophical, who's to say what's right and what's wrong? No one, except maybe God if there is one. But even then, how do we know that God's "right", since "right" is only a concept of the human mind.