What we haven’t figured out how to make sense of yet is the fun that many Americans act like they’re having with the national fracture.

Why is the author confused about this? The people who are having fun are doing so because they see a correlation between the degree of fracture and their own wellbeing (political, economic, strategic). They don't feel invested in the status quo (perhaps quite legitimately) and see more opportunity in either a fragmented and chaotic polity or a new status quo in which they occupy a higher position.

Sure, you could say 'but this makes no sense, everyone will be worse off', but this is self-evidently not the case. Revolutions, civil wars, etc. have winners and losers. Most end up as losers, but some people make out like bandits. And people who are losing (or who just feel like they're not winning enough) under the current or foreseeable future systems feel incentivized to bet on something different.

The point of [role playing games] was not to beat your opponent but to share in the thrill of making up worlds and pretending to act in them.

No. The point of role-playing games is to experience freedom of action by making up worlds with fewer constraints - but with the validation that comes from sharing the process as opposed to daydreaming. For kids and teenagers the constraints might be structural ones like having to go to school and follow arbitrary-seeming conventions. For adult enthusiasts the constraints might be economic reality - without access to unusual resources or talent, the options and payoff horizons of everyday life may seem very unsatisfying.

You can see a sort of meta-argument about this in the rise of boring simulation videogames, which let you experience a dull job or social obligation in all its futility and tedium, with the payoff for the player being that when you get sufficiently bored, you are allowed to stop playing and nothing bad will happen - whereas rejecting things that seem dysfunctional or futile in normal life might be economically disastrous.

The main change wrought by the internet has been the widespread realization that political representatives and social elites are not the highly refined output of a meritocratic selection process, but often mediocrities that lucked into assortativity and network effects. Those who perceive social and economic institutions to be gamed in various ways are incentivized to rewrite the rules of the game in their favor, and are enthusiastic in proportion to their skill and expectations of success.

Think of the old not-really-a-joke about the two campers whose sleep is disturbed by a bear. One stirs up the fire with the plan of scaring the bear away, the other starts putting on shoes. 'Why are you putting on shoes? you can't outrun a bear' says the first camper, to which the second replies 'I don't have to - I only need to outrun you.' I describe it as not-really-a-joke because this sort of story can be a subtextual way of communicating that the teller prefers to minimize their own risk rather than pool it with someone else, and disavows any prior assumptions about teamwork or loyalty. Similar examples include the frog and scorpion (frog gives scorpion a lift across a river; scorpion stings him because 'it's in my nature' although this makes them bother worse off) and the woman who picked up the snake (which then bites her and says 'what did you expect, I'm a snake' and slithers off in search of another victim).

Often, people are communicating their preferred or idealized outcomes quite clearly, but their audience are confused or unhappy about it and respond with appeals to decency, reality, science, orthodoxy and so on. Such appeals are often a coping mechanism to avoid the unpleasant implication that the communicator is going to bail on, sabotage, or attack them. Appeals to moral or existential authority are only forceful to the degree of mutual connectivity, and miss the fact that in these story examples the parties are isolated and there's nobody around to intervene.

To sum up, when people set out to reshape reality it's often because they see advantage in doing so, and disagreements about rationality often mask a conflict of values.