Okay, so there can still be two main parties, but isn't the idea to allow third party candidates to run without taking votes away from the most similar candidate? I haven't studied all the different forms of voting [1]. I know there isn't one that's perfect, I just think we can make some improvements on what we have now. I am not ashamed to admit most of my understanding of this comes from CP Grey's animal kingdom =).
EDIT: Just read a bit about approval voting and score voting. I guess I'll suggest those next time instead of mentioning IRV.
[1] https://en.wikipedia.org/wiki/Voting_system#Compliance_of_se...