Heina Dadabhoy has written a good article about the Preachy Polyamorist trope: Why Are Those Polyamorists So Damn Preachy?, which is enhanced by some of their earlier observations in When the Monogamous Bait Poly Smugness. I recommend reading both. I pretty much agree. And their latest has inspired me to write my own thoughts down, which expand on theirs, but also at points diverge from theirs.
Before I proceed, though, a trigger warning: I’m going to get all preachy about polyamory. In fact, I’m going to be a counter-example to Dadabhoy’s otherwise valid generalization, and become one of those “rather smug-seeming polyamorous people” who might leave you “feeling judged.” If you want to stop your ears against that, depart now. You were warned.