[LeifCarrotson]

It very much depends on the nature of your work.

If manual input can generate undefined behavior, you depend on a human making a correct decision, or you're dealing with real-world behavior using incomplete sensors to generate a model...sometimes, the only reasonable target is "fail gracefully". You cannot expect to generate right outputs with wrong inputs. It's not wrong to blame the user when economics, not just laziness, say that you need to trust the user to not do something unimagineable.

I think this is the kind of situation where a little professionalism would have prevented the issue: Handling uncaught exceptions in your threadpool/treemap combo would have prevented the problem from happening.