unfortunately you fall victim to one of the classic blunders...sorry wrong movie anyway the problem with what you're saying is that you view the public as having a single feeling of what is in their interest and that democracy can every adequately represent this public interest. Unfortunately that's impossible, Kenneth Arrow, won a nobel prize for stating essentially that no method of aggregation can come up with a completely fair estimate of the public interest. In large part because of cycling ala one person likes a>b>c another b>c>a and a third c>a>b in this sort of scenario there is no such thing as a condercet winner(one that beats all the others) because B beats C, A beats B and C beats A. in reality no method including instant runoffs is completely fair they just bring about a different winner without improving the overall "fairness" level additional arguments can be made because of strategic voting where individuals purposely misrepresent their vote in order to avoid their worst outcome.