> human interactions are positive to participants pretty much if and only if those interactions are repeated

> One-off interactions are almost invariably toxic

I think these claims are too strong. I can believe that there's less incentive to treat people well when you don't expect to repeat interactions.

To give a mundane counter-example: last week I had a flight where I chatted on-and-off with the person next to me. I had zero expectations of repeat interactions with them following the flight, and it was still a friendly and courteous exchange, on both sides.