> Is it a bug if it never happens? Another way to say it, would you pay money to prevent a problem you don’t have?

Let me rephrase that: Is it a bug if I don't know about it? Another way to say it, would you pay money to prevent a problem you're not (yet) aware of?

Saying the bugs "never happen" is basically saying "I always write bug-free code."

I feel languages that don't have type checking (or where it's sloppy), force developers perform semi-automated testing (i.e. unit tests to catch type issues) when they could have systematic, fully-automated testing (for type issues, at least)

Right, but some people are doing data wrangling by themselves with python in a jupyter notebook. These aren’t production systems, and static type checking slows you down without adding much value.

That’s all I’m saying, the data analyst that has some edge case “bug” that never gets executed probably shouldn’t pay the upfront overhead cost of type checking.

Is having buggy, unused code lying around a good thing?

It’s not always bad, and dealing with it has a cost. The cost is not always worth. It may be worth it most of the time, but not always.