Casting errors to exceptions (panic/recover) are considered a valid approach in Go within your application logic. Its built-in HTTP handlers will even 500 out of the box if a panic isn't recovered beforehand.

But other layers of abstraction lose their utility value if they start to make assumptions about the caller. Maybe in your web service a 50x stop the world error is all you'll ever need if there is a database error, but the next guy using the code for another purpose could have very different requirements and when you have to actually deal with errors, exceptions become a royal pain very quickly. As such, the official line is simply that you shouldn't let errors casted to exceptions cross package boundaries.

But, again, Go isn't really designed for stop the world programming and it's okay to use another tool if your problem space is suited to stopping the world.