Also I remember reading somewhere that the earlier you find the error the cheaper it is to fix it.
> why did my app just disappear, did I do something wrong?
Usually operating system reports that there was an error in the application. If the application crashes often, the users will complain to developers and they will fix it.
> Debuggers are a terrible user experience, we don't need to force every user to live in a debugger
You should test your app properly before releasing it.
> There are disastrous consequences to bad multi-threaded code during "fail fast" teardowns of threads not privy/cause to the error.
I cannot agree with this. Usually the OS releases all locks, closes all files, frees memory when the process terminates. I don't see what can go wrong here and how you can get a deadlock because some process has terminated. Also if you use locking you should add some kind of timeout. For example, MySQL has lock timeouts and can even detect and fix deadlocks.
> "Fail fast" in day-to-day operation isn't the right solution, at the very least for making users possibly hate you because you'll never properly handle 100% of exceptions
The users will probably hate you more if the app will silently hang or show incorrect data.
Sure, fail fast is very useful in debuggers to help a developer find and fix problems. But this is why we have debuggers. Debuggers are a terrible user experience, we don't need to force every user to live in a debugger and decide themselves which errors matter.
Not every exception is "fatal" and "might look like it is working ok" is often good enough in the pragmatic real world where you can't control everything.
Also, just because you've never accidentally caused a machine to BSOD on a deadlock or catch fire from an improper halt in a "fast fail" of multi-threaded code, that just means you are one of the lucky ones. There are disastrous consequences to bad multi-threaded code during "fail fast" teardowns of threads not privy/cause to the error. There are enough nightmare scenarios to keep a multi-threaded programmer up at night.
I appreciate your concern that developers sometimes ignore errors they should fix instead or handle more appropriately. "Fail fast" in a debugger works to help that. "Fail fast" in day-to-day operation isn't the right solution, at the very least for making users possibly hate you because you'll never properly handle 100% of exceptions.