<blockquote>Yes. By far. Again, you seem to be - I suspect because you’re wired into the subculture - grossly overestimating how many genuinely polyamorous people there are.</blockquote>
Who counts as genuinely polyamorous? People who are aware of it as an option and currently feel confident suggesting it? If so, I agree they're few in number. But if that also includes people who'd seriously examine their barriers to it in a non-threatening environment in which there's no stigma against polyamory, I expect that number would be significantly larger. Quite possibly still a minority, but not a small one.
<blockquote>destigmatizing polyamory would mean monogamous relationships essentially constituting a minimum-member poly relationship that isn’t looking to expand. “Negotiating the kind of relationship you want” is inherently a polynorm, wherein the mere existence of negotiable terrain pressures people to accept negotiated relationships they’re unhappy with.</blockquote>
If people negotiate themselves into a monogamous relationship, how is that negotiation a poly norm? Depending on what you mean by "isn't looking to expand", your description sounds like current monogamy, except negotiated explicitly - it isn't looking to expand because its members don't want it to and have promised to each other not to take other partners.
As for people negotiating themselves into something they don't like, compare to the status quo, where people are stuck with the default - what are the chances that it's optimal, or even that it's better than people could negotiate for themselves? BTW, it's not just monogamy vs polyamory that could be negotiated, but other aspects of the relationship as well. Yes, some people could put themselves in a worse position, but how strong of an argument is that? Do you want an unchangeable one-size-fits-all agreement in other areas of life as well, such as employment, loans, etc?
<blockquote>I don’t know about necessarily, but pragmatically: because they’re the vast majority and their misery from not getting their way is vastly larger than that of the polyamorous.</blockquote>
But I'm not forcing the monogamous to be polyamorous. If they have such a strong preference for it that they'd be miserable otherwise, they shouldn't agree to polyamory and only date other monogamous people. If they're as large of a majority as you claim, that shouldn't be a problem.