I think we can all agree that once you throw prize support into the equation, some people will get ugly.
Prize support or not, some people will always get ugly. Some people quite simply can't handle competition, and others can. I've seen plenty of cases of people blatantly cheating when the only thing on the line was bragging rights.
Heck I've seen people cheat at Solitaire, or get so upset that they nearly flip the table... So no prize support does not inherently make people worse, it only intensifies their behavior.