A bit of a pushback, if I may: confirmation bias/motivated reasoning themselves only arise because of an inherent, deep-seated, [fairly likely] genetically conditioned, if not unconscious sense that:

A. there is, in fact, a single source of ground truth even, if not especially, outside of regular, axiomatic, bottom-up, abstract, formalized representation: be it math [+] or politics [-]

B. it is, in fact, both viable and desirable, to affiliate yourself with any one/number of groups, whose culture/perspective/approach/outlook must fully represent the A: instead of an arbitrarily small, blind-sided to everything else, part of the underlying portion it is most familiar with itself

C. any single point/choice/decision/conclusion/action reached must, in itself, be inherently sensible enough to hold for an arbitrarily significant period of time, without any revision or consideration of the opposite/orthogonal perspective; this one, in turn, might itself stem from an assumption that:

D. the world must be either a [1] static entity, fully representable with an arbitrarily large set of beliefs, attitudes, and considerations; or a [2] dynamic, yet inherently mechanical, following the exact same static laws/rules/patterns in each and every aspect of itself: be it physics or society; these last ones can be safely assumed to be never-changing and, once "understood", always reinterpreted within the exact same light as in the original interpretation of the time

E. whatever the kind of entity it is, any particular snapshot of the linguistic and/or symbolic representation of it is, at every moment, fully capable of describing it, without coming up short within any single aspect of it: an assumption, if you will, that there no "3x+1 Conjectures" the limitations of our cognitive/representative tools in the present would not be able to figure out

Biology-wise, the B might be strong enough to easily overpower, without any of our conscious awareness, the rest of them. Yet even discounting that: the motivated reasoning and the desire to adhere to whatever stance has been reached already themselves stem, fundamentally, from the sheer human arrogance in regarding whatever was [conceived/perceived/assimilated/concluded] as fully sufficient both for what is in the present, as well for what will be yet, going forward. 

That arrogance, in turn, anchors our cognition; which promptly short-circuits itself into whatever Weltanschauung our general A-E'sque attitude of the day lines up to, in attempt to save energy on rather costly and, given A to E, completely wasteful brain cycles. MR/CB is merely an effect of it all.

P.S. Two upticks from me, regardless. The links were much appreciated. Would gladly hear any of your additional thoughts on the matter in a fully-sized post/article/whatever you call it here.

Appreciated: both footnote [corrected] and bluntness-wise. The whole post came out of somewhat of a hydraulic press for me, so that statement [among others] seems quite fitting. Might end up rewriting or heavily editing a few portions here and there in the future, though. For now, I definitely need a break and some time to recharge. One week of back and forth in order to compile and structure it all was enough.

Fair point. Didn't think it through that much when I first drafted it. Still, multiplication has its time and place - at least for a portion of them.

You can categorize an "idea", broadly speaking, into one of the two: a one-off change in state (e.g. any project), or a repeated execution of a particular behavior (e.g. building a new habit).

For a project, addition may be more suitable. Could you say the same about habits, though?

Semantics. What do we, or they, or you, or me, mean when we talk about "happiness"?

For some (hedonists), it is the same as "pleasure". Perhaps, a bit drawn out in time: as in the process of performing bed gymnastics with a sufficiently attractive member of the opposite sex - not a moment after eating a single candy.

For others, it's the "thrill" of the chase, of the hunt, of the "win".

For others still: a sense of meaningful progress.

The way you've phrased the question, seems to me, disregards a handful of all the possible interpretations in favor of a much more defined - albeit still rather vague, in virtue of how each individual may choose to narrow it down - "fulfillment". Thus "why do people solipsistically optimizing for hedonism are actually less happy?" turns into "why do people who only ever prioritize their pleasure and short-term gratification are less fulfilled?" The answer is obvious: pleasure is a sensory stimulation, and whatever its source, sooner or later we get desensitized to it. 

In order to continue reaching ever new heights, or even to maintain the same level of satisfaction, then - a typical hedonistically wired solipsist will have to constantly look for a new "hit" elsewhere, elsewhere, elsewhere again. Unlike the thrill of the "chase" however - there is no clear vision, or goal, or target, or objective. There's only increasingly fuzzier "just like that" or "just like that time back then, or better!" How happy could that be?

[1] Can't they both be not objective? Why make it a point of one or the other? A bit of a false dichotomy, there. 

[2] There is no single "Internet" - there are specific spaces, forums, communities, blogs, you name it; comprising it. Each has its own, subjective, irrational, moderated (whether by a single individual, a team, or an overall sentiment of the community: promoting/exalting/hyping one subset of topics while ignoring others) mini/sub-culture. 

This last one, furthermore, necessarily only happens to care about its own specific niche; happily ignoring most of everything else. LessWrong used to be mostly about, well - being less wrong - back when it started out. Thus, the "rationality" philosophy. Then it has slowly shifted towards a broader, all-encompassing EA. Now it's mostly AI. 

Compare the 3k+ results for the former against the 8k+ results for the latter.

Every space is focused on its own topic, within whatever mini/sub-cultural norms are encouraged/rewarded or punished/denigrated by the people within it. That creates (virtually) unavoidable blind spots, as every group of people within each space only shares information about [A] its chief topic of interest, within [B] the "appropriate" sentiment for the time, while [C] contrasting itself against the enemy/out-group/non-rationalists, you name it. 

In addition to that, different groups have vastly different [I] amount of time on their hands, [II] social, emotional, ethical, moral "charge" with regards to the importance they assign to their topic of choice, and emergent from it come out [III] vastly different amounts of information, produced by the people within that particular space.

When you compile the data set for your LLM, you're not compiling a proportionately biased take on different topics. If that was the case, I'd happily agree with you. But you are clearly not. What you are compiling is a bunch of biased, blindsided in their own way, overly leaning towards one social, semantic, political, epistemological position; sets of averaged sentiments. Each will have their own memes, quirks, "hot takes". Each will have massively over-represented discussions of one topic, at the expense of the other. That's the web of today.

When you "train" your GPT on the resulting data set then, who is to say whether it is "averaging" the biases in between different groups? Can you open up any LLM to see its exact logic, reasoning, argumentation steps? Should there be any averaging going on, after all - how is it going to account for disproportionately represented takes of people, who simply have too much time and/or rage to spare? What of the people, who simply don't spend too much on the web to begin with? Is your GPT going to "average in" those as well, somehow?

What would prevent the resulting transformer from simply picking up on the likelihood of any given incoming prompt matching the overall "culture" of any single community, thus promptly completing it as if it was a part of an "average" discussion within that particular community there? Isn't it plain wishful, if not outright naive*, to imagine the algo will do what you hope it will do - instead of what is the easiest possible thing for it to do?

* the fact a given thought pattern is wishful/naive doesn't make you wishful/naive; don't take it personally, plz