(Your argument assumes that someone likes being second-best, which I still contend is pretty bizarre.) [...] someone who is "secondary" to one person can be "primary" to another. [...] This means that it can be potentially fair, but it's still incumbent upon the polyamorist to ensure that [...] no one is being taken advantage of.

(Data point: I am one of Alicorn's former secondaries and was not in any other romantic relationships at the time, and I can testify that I did not feel exploited. I have no particular reason to care about what you consider bizarre or unfair.)