Most of the young or cartoony Sweetiepies are convicts that were sent to the Valley to be rehabilitated by the Ruby Pure Heart, thus a need for the barrier.
Sweetiepies that look most like normal animals were former residents that were forced to live with the convicts, the older a resident the less Ruby affects them, e.g. Marion and Honey look almost like Sweetiepies since they're young while Farmer Bun and Bait-Shop Bub look almost normal is because they were older before the Ruby activated.
Reason why Pinky and Slim are so chaotic is because they were the newest convicts to join the Valley and so were first to had a head start to reverting back, behind them was Chubbums.
Most Sweetiepies are chaotic because the Ruby considers everyone a criminal and thus the transformation process is a bit flawed.
Snugglemagne is actual royalty but was sent to the Valley to act as the Warden so that he wouldn't meddle in his families affairs.
Ruby doesn't affect people living in the castle and outside the Valley's boundaries, the reason the King acts as a Sweetiepie is because he's a giant LARPer.
The reason Badgeclops feels uncomfortably warm and why he sometimes acts out of character is because the Ruby knows that he's a criminal and is trying to rehabilitate him, but because of it's damage and because Badgerclops rarely leaves his house it can't.
The Ruby purposely attracts monsters to wipe out the Valley because it's one of it's failsafes in case the barrier falls.