Quote ulTRAX:And IRV still gives the two major parties the advantage and may in fact perpetuate them in place.IRV may encourage the creation of other viable third and fourth parties. But the problem with IRV is that those who vote for these parties are surely to lose and therefore their second choice vote is probably just going to be the lesser of the evils. So without ever winning elections there's little advantage to joining these parties and they are unlikely to grow to the point they could break through to get a plurality. This may have the unintended consequence of perpetuating the grip on power by the original two parties similar to how they now take for granted Progressives who routinely hold their nose and vote for Dems. Unless there could be SO many parties, a 3ed party could break through and win that plurality.
In contrast with proportional representation there are less obstacles to 3ed parties. If a Progressive 3ed party earned 20% of the vote, they'd get 20% of the seats. People can vote their conscience and be sure to get some REAL representation for their beliefs. With IRV the winner knows s/he won only with the half-hearted support of a 3ed party who held their nose.
While IRV can prevent the so-called spoiler effect, it's unlikely to change the dynamics of our system or its underlying defects.