Someone will have to explain to me why stealing signs is so bad. Is it only because it's sneaky and underhanded? Really, it's effective coaching. If you can figure out the signs and give your team the advantage. What am I missing?
It's not uncommon for a runner on second to try to suss out the catcher's signs and relay them to the batters. In the case of the Red Sox, it's that they were literally using the video replay room, which is not only a violation of the Official Rules, but prior to the 2018 season, Manfred sent out a memo to all 30 teams that basically said "I will fucking bury you if you use video / replay to steal signs."
Edit: Same reason why in the NFL you can't tape an opponent's sideline (oh hi Patriots) and coaches don't get to see real-time video, only photos, on those tablets they all have on the sidelines. You can get ahead by intuition and talent, but you don't get to goose things up with a tech advantage the other team doesn't have.