Loss aversion, which wanted to restrain me from giving up the potential to date people who would consider ever having been poly a dealbreaker. (Note: I implemented what I believe to be a reversible hack, so I didn't have to worry about not being able to enter a monogamous relationship if that ever seemed called for).

"Who exactly are these people? Do I know any of them? Not any who I'd want to date in any recognizable scenario. Okay then, the class as a whole is to be counted a less valuable opportunity than the class of poly people (which notably includes MBlume)."

Past behaviour is an excellent predictor of future behaviour as Roissy/CR would love to point out and I would agree. If one prefers monogamy it is not that irrational to seek people who lean towards it. Though in practice most people won't bother so I think your thinking is solid on this point.