Negative Campaigning
The winner-take-all, first past the post method of elections has led to a dramatic descent into the worst forms of partisan, negative campaigning and mud-slinging.  This is mostly a result of the strategies that have recently been very successful in winning elections: viciously attack your opponent and whip up as much support from your base voters as possible. 

IRV is a way to change the equation.  In an IRV election, a candidate can benefit from maintaining good relations with their opponents.  A candidate wants voters who don't whole-heartedly support them to rank them as their second choice, greatly improving the candidates chances in the event of a run-off.  The best example of this is the recent IRV elections in San Francisco.  According to the New York Times, candidates in the race for seats on the County Board of Supervisors held joint fund raisers and openly praised their opponents.  This atmosphere of respect and co-operation leads to debate on real issues facing voters instead of personal attacks and partisan rhetoric.

[Read the New York Times article on the San Francisco elections here]