I would ageee with you for cases where both sides had a strong argument, but in Snapchat’s case everyone was complaining about the new UI, so I’m not sure how to describe that sense - people who complained are from all different ages & backgrounds so it’s not like they had UI design experience or anything - “common sense” is probably the only thing they all had in common and that thing alone was enough for them to determine the UI sucked.

In this case, simply doing some basic user-testing would’ve been considered common sense and would’ve brought up the problem immediately.