Can people go on a short-term mission trip and and return unchanged? Yes, they can. Can people go on a short-term mission trip and return changed? Yes, they can. I have seen both.
This article looks at the question, "What value does short-term mission trip have for its participants?" And, unfortunately, like most journalistic pieces, it never really gives anything close to an answer to the question.
Rise of sunshine Samaritans: on a mission or holiday? | csmonitor.com: "'We justify our efforts by saying [youth] will come back and make a difference in their own communities, but the research has demonstrated it's not happening,' says David Livermore, an evangelical scholar at Grand Rapids Theological Seminary and author of a new book, 'Serving with Eyes Wide Open: Doing Short-Term Missions with Cultural Intelligence.' 'Kids are going down and 'loving on' Mexican kids for a week and then coming home and being the same racist white kids they were toward their Latino classmates before they went on the trip.'"
I think the answer lays somewhere in between. Short-term mission trips combined with a missionary life-style back home is best. At the church I planted, I attempted to move people from being spectator Christians to seeing the value God places on lost, broken, poor, hurting people. Not just the people they would meet on a "short-term mission trip," but also the people they meet in every-day-life.
Short-term mission trips have the potential to change someone's life, but that trip is not enough. It must be developed into a missionary life-style. Check out www.servantevangelism.com.