Rich people generally help this country out far more, not only pay more tax, but creating jobs and providing skills. We lose a lot of these people and there business to foreign countries with lower tax.
The rich benefit more from society than they give back. They're rich after all. As for people threatening to leave the country is an empty threat. It always has been and always will be. Did you know that despite the bleating about the bank bonus tax, the number of bankers leaving the country to work elsewhere has actually fallen not risen?