The bandit stole the jewels to prevent the English from being able to bribe the authorities, he wasn't out to get his hands on the gems, he wasn't out to just steal from the English, he was out to prevent those gemstones from reaching their destination, his motice was political, not profit. Joker in the movie was also a political actor, he was out to save Gotham, not destroy it, he did so by accomplishing everything that batman could not. He took down the mobs and gangs, he took out the corrupt police officers, he ended the crisis of vigilantism by making batman hated and harvey dent into a beloved figure who would never become corrupted by his latent issue with extremism, and he then made the people of Gotham sympathetic to the criminal population who committed crimes put of a need to survive in a desperate situation, he even successfully took out the corrupt heads of corporations. The joker has a plan, and it worked gloriously, by the start of the next movie, Gotham wasn't perfect, but it was well on it's way to recovery now that the core causes of its decline had been addressed. Then Bane shows up with the league of shadows in the next movie, and since the league of shadows uses perfection as its standard, and Gotham had not yet gotten rid of its image as the city that represents wickedness, the league decide to take it over and destroy it after making an example of it, so as to scare the rest of the world into compliance with the leagues unrealistic standards of goodness, basically using Gotham like the Bible used Sodom and Gomorrah.