@freemo why do you call it a myth? From what I understand, the mechanics are such that there are practical risks involved, concerning votes cast to "lesser"/"minor" parties concerning wasted/lost votes when the minor party loses.
Its a myth because it is only the beleif in it that creates the effect at all. If no one thought there was a two party system there wouldnt be one.
Few points of evidence:
* Before people in the USA thought there was a two party system, there wasnt. Despite the voting system not having significiantly changed prior to the last 100 years the primary parties changed all the time. Throughout US history the 2 dominate parties have been replaced 8 times
* Other countries with a first-past-the-post voting system do not show a tendency to a 2-party system. There are countless elections around the world using this approach that dont consistently have the same 2 parties win
* Even if you model out the debunked theory claiming FPTP results in 2 party it doesnt make sense. Under that model it would only produce an illusion of a two party system (where the real support concentrates in the top 2 in votes). Nothing about the model would keep the same 2 parties in power, it would just cause the switching between parties to be abrupt (third parties with little votes in previous years suddenly jumping to 51% support over a single election). So even in pure theory if we accept the myth in that context it is still not real in any meaningful way.
@freemo hmmm.. you're making good points. I think it is a bit of a sinkhole that if you get stuck with two major parties it's hard to get away from that.
The math argument bothers me, where: if A is the least attractive but major, B is moderately attractive and major, C is most attractive bit minor. If you vote for B, you have reasonable chance, but if you vote for C and lose, then your vote that otherwise would've gone to B is now lost, therefore directly benefiting A.