Do what? Write an extra check to the IRS?
I imagine members of a group like this are already involved in putting their wealth to good use, but if not, then sure, they could do more. Do you know that they don't? They're at least spending part of their time and treasure advocating for fairer sharing of burden.
But the point of this is not only their individual contributions, it's in putting to work the wealth of everyone else who have much accumulated as well.
I even remember reading about some of their whinging that he was "unfairly" competing because he wasn't trying to wring every penny out of it.