There's a certain logic to "hope for the best, prepare for the worst", but I get the impression that for a lot of people, thinking about horrible things is simply instinctual and the reasons they give for it are rationalizations.

I resent the suggestion that I instinctively think of 3^^^3 dust specks! I have to twist my cortex in all sorts of heritage violating imaginative ways to come up with the horrible things I like to propose in goofy hypotheticals! I further assert that executing the kind of playfully ridiculous-but-literal conversation patterns that involve bizarre horrible things did not help my ancestors get laid.