I have yet to see a story about someone who was detained and not allowed to return to their home country of Canada or Germany who wasn't also either accused of

I have yet to see a story about someone who was detained and not allowed to return to their home country of Canada or Germany who wasn't also either accused of a legitimate crime or otherwise violate the terms of their visa in a clear and obvious fashion. Even in those cases though, you are usually sent back to your home country as the punishment. It seems reasonable that border control will someday make a mistake, detain someone, and then let them go, but this is rare enough that there aren't any recent instances of it, and it's not an ongoing problem.