In a movie from a few years back, three men roped together are walking on the glass roof of a shopping mall, at least three stories high above the mall floor. Suddenly the glass on which they are walking cracks, and two of the men fall through, leaving one man on the roof to hold the other two up and keep them from falling to their deaths. The man on to the roof doesn't have enough strength to pull the other two men to safety, and soon the glass beneath him is cracking under the weight of the three men, so that in a few more seconds it will shatter, and all three men will fall to their deaths. The man at the bottom of the rope realizes that either he goes, or they all go, so he cuts the rope binding himself to the other two men and falls to his death, thus saving the lives of the other two men.
It has never occurred to me to think of the man who sacrificed himself so the other two men could live as anything other than a hero. After all, he was bound to die no matter what, but through his selfless act he prevented two more deaths. But there are others who would argue that the third man actually committed a mortal sin in causing his own death -- i.e., it was suicide, and suicide is never justified, even if one's death is inevitable and hastening that death may save the lives of others. They argue instead that the only moral course of action would have been for the third man to do nothing, and consequently all three men would have died. Are they correct?