There are plenty of legitimate reasons why I'd like a time machine. Each one's for my own benefit; I believe too much in time travel paradoxes to assassinate Adolf Hitler or Idi Amin or anything like that. Sure, there's a pretty good chance the deaths of millions of people would never take place, but there's an equally good chance that a disaster of even greater proportions might transpire. No, I leave the big stuff in history to the course of history.
I would like to travel back in time so I could purchase Coca-Cola stock in 1919 during it's initial public offering. Then I'd likely head futureward and find Jackson Pollock to pick on him because his paintings were so terrible and he was a big jerk. Then I'd probably get something to eat somewhere and go home and go to bed. That's just one of the jaunts I have planned after everything ... falls into place.