Joe, Haiti was a PEACEKEEPING mission, intended to stabilize the country. A HUMANITARIAN mission, in which we provided medical supplies and food. The people were starving, so of course they tried to steal food. You can't go into a country offering to help, and start shooting people.
You have to understand the PR involved. Starving civilians getting gunned down by soldiers doesn't play well on the evening news. Also, in the roleplaying scenario I mentioned earlier, my "murder" touched off rioting in our simulated community.
Yes, a soldier or marine has to be a good killer, but they also have to know when NOT to kill, and they have to have the tools necessary to respond to less than lethal and civilian situations.