They already pay far far more than everyone else, in total amount, percent of income, and even percent of income relative to total income. By wide marginswell I think the are morally obliged to pay more anyway - which is the spirit of the OP's idea. It's not like the government completely wastes every single tax penny. And even if they would, the more you have the more you can miss.
Furthermore, not only does this depend on the country you live in, I know from first hand experience tax avoidance is real, and mainly with richer people because they can pay others to do it for them. Now if they try to avoid taxes n order to give that money to the poor, I'm all good with it. But chances are they don't, in which case I'd rather let the government have it instead of it resting on the bank or being used to buy an environmental disaster like a speedboat :P
