[rjf72]

Instant runoff only really resolves the spoiler effect. I think it's extremely unlikely we'd see a third party come even close, including with instant runoff, to taking power. I'd look at the problem numerically. Imagine a state has 100 representatives sent to congress. And we know this state is let's say 30% republican, 30% democratic, 20% libertarian, 20% green. What would you say their representation should look like? Everybody's going to say the exact same thing: 30 republicans, 30 democrats, 20 libertarians, 20 greens. The only problem is that you only get that distribution with proportional representation, which as a nice side effect also would do away with gerrymandering since you don't need to carve a state up into representative districts anymore.

The downside here is that proportional voting doesn't stand a bat's chance in hell of ever getting enacted because it really would lead to a major upheaval in DC. And the very people that would be 'losing their jobs' are the ones that'd need to work to pass it, which would be a tremendous undertaking. You'd need a 2/3rds majority in both the house and senate to start the process, and then you'd need 38 of the 50 states to ratify the change. And at the end of this process the two major political parties, who are in control of every single major political body in the United States, would have just ceded a tremendous amount of power.