The Bluebloods have offended, insulted, wronged and in some cases harmed many, many ponies, but they remain immune to retribution. They own the nobility, host top-notch security and know the location of every high-end criminal from Las Pegasus to Manehattan.
Sir Karet Fancypants de Gelding is done with it.
What threat could a collection of straight-laced Canterlot Shires citizens — most of whom have never even contemplated breaking the law before — possibly pose? How could anypony even make a dent in their vaults and reputation?
Twenty-million Bits and more says it's worth a shot.