the below video is about the cinco de mayo referendum in the UK, but it also gives a pretty concise explanation of why alternative voting would be a good thing to institute here in the u.s. as well.
of course it will never happen here. both major parties have too much to lose if it did. the democrats want to keep the "hold their nose" votes from people who would otherwise be greens or other more liberal third party voters but who don't want to "throw away" their vote. likewise, the GOP wants to keep libertarians and other far right fringe people voting for their party even if in their heart-of-hearts they would rather go somewhere else. (it also suits the GOP just fine for the likes of the greens to never get any real power). but i am still very curious how the last few elections would have played out differently if there were an AV system in the u.s.
