re: What is missing inside people who intentionally start/spread disinformation just for fun?

Even if you can’t see it, there is always an agenda behind inventing lies.

Sometimes, “disinformation” is really just conjecture. Someone sees something happen that conflicts with their world view, so they try to hypothesize explanations for it that fits within their worldview. “We are at war with Russia/China” is their world view. So, when they see a big infrastructure failure, they assume it means “this is an act or war by Russia/China”.

Some conjecture is healthy for society because the truth is often not the first thing one would assume looking at a situation. However, too much conjecture can lead people down some pretty bizarre rabbit holes. At some point, you’re just reinterpreting events to support your ego rather than to find truth, and that’s when it becomes a bad thing.

A purposeful lie like “he’s cheating on her” is probably motivated by that individual wanting to destroy that relationship. Either they want the girl/guy for themselves or they’re jealous of the couple’s happiness and want them to no longer be happy.

A lie about a business could be used to extort them for money, help competitors, or hurt the people who own it.

Lies could be for petty revenge, protecting oneself from consequences, or for justifying complex geopolitical agendas.