The logic of consumerism is to weigh all your choices and find out what you really enjoy.

What exactly are you proposing as an alternative to that process? Your whole post seems to be based on equating "explore all options and maximize" with "the logic of consumerism", but while the former may well be necessary for the latter, it's not even close to sufficient! To a large extent, that's simply the logic of decision-making.

The main difference is that polyamorists want to do this in the open, rather than in secret, which is to say that the difference is primarily that polyamorists want to be nonconformists.

So, the desire to be honest can't have anything to do with it?

Or are you convinced that the world is so fundamentally dishonest that honesty is innately equal to non-conformism?

I thought the major argument for polyamory was that some people are happier living that way.

Your first argument suggests that you find such arguments repulsive, but I can't see why.

The major argument for polyamory isn't that it's subversive, though I'm sure some people get a kick out of that.

However, I don't think polyamory is at all mainstream, even though it's closer than it was in past decades. Note that none of those accused in political sex scandals have said that they had an non-monogamous agreement with their spouse, >2 marriages are used as a slippery slope argument against homosexual marriage, and afaik, the only popular fiction about polyamory presents it as very unusual.

If you're looking for a one-size-fits-all set of rules, then polygamy - and, in fact, most forms of social interaction, including monogamy, if you're interested in doing it well - is probably not for you.

The freedom that's noted as a trait of polygamy isn't the freedom from complexity (it's complexity that leads to the "rules"), it's the freedom to choose the kind of complexity you want to deal with, and how you're going to deal with it.

So we're promised freedom, and we end up with an almost Kafka-esque nightmare of never-ending series of rules that we can never be sure we truly following correctly since every situation is different. In contrast, the traditional model of infidelity has historically had one very simple rule: be discreet. Aside from that, anything goes, including sexual acts that have been considered illegal: interracial sex, prostitution, homosexuality, etc.. To be absolutely clear, I'm not at all advocating this, I'm simply pointing out that the claim that polyamory is about freedom while monogamy is about constraints falls apart immediately on serious inspection. If anything, the opposite is true.

I was initially going to respond "Constraints that you participated in the writing of and explicitly agreed to don't go against the notion of freedom at all, certainly not compared to ones you have no say in and little choice to decline," but it seems you're coming at this from a rather different angle. You are considering the constraint of monogamy not as "be monogamous (details elsewhere)", but rather as "be discreet about polygamy". This has several problems, SFAICT.

We can apply this sort of level-jumping operation to any rule - "Do X" becomes "Be discreet about violations of X" - but these aren't the same thing, and it is far from obvious that the latter is so. A real instance of the latter might be, for instance, how Spartan boys were taught to steal food - they were beaten if caught, because they were supposed to avoid getting caught. But, the general reaction to learning about violations of monogamy seems to generally be, "They did that?" rather than "They let themselves get caught?" or "They told people", which suggests that most people have the simpler rule in mind. Or, even if they don't, they certainly want to appear as if they did. Which either means they think most people have the simpler rule in mind, or the whole thing is one large mass hypocrisy in which everyone knows the actual rule is "be discreet", but admitting this would be itself a violation of the rules. I suppose the latter isn't too implausible, seeing that a number of things do seem to follow that pattern... but there will always be people, the "nerds" in Eliezer's terminology, who actually believe what they're told, and who won't be in on it, and who actually will be using the basic rule. So even in the latter case I'm not sure you can claim that's the actual rule. (In addition, in the latter case, the acknowledgement of the "be discreet" rule is unconscious, which doesn't sound like what you're describing above.) Though maybe I've missed a few cases?

OK. That's problem number one. Problem number two is, once you're acting within the bounds of "be discreet"... what are you actually going to do? You need more than one person for sex, and that (I should hope) means some sort of agreement about what's actually going to go on. In short, we're right back to square one - the freedom of "be discreet" is no different from the freedom of, well, open freedom, except that the former is hidden and the latter is not. Give people freedom to interact with each other, and they'll want some sort of assurance of what other people will do, and will start making promises and contracts.

Problem number three is that it's hard to see this as a solution when it's fundamentally dishonest, but I guess that's obvious.

Problem number four is that it's arbitrary. You said the freedom is to "be discreet". Be discreet about what? About violations of some rule. What rule? Does it matter? You're talking about violations of monogamy, but your entire argument, if valid, would go through if that were replaced by polygny or any other rule. Your argument doesn't support monogamy - it supports secrecy, and that's all.