I find this discourse incredibly frustrating. I don't like billionaires, and I would prefer they give away their money more rapidly. But they are following that laws that exist just as much as the rest of us. We don't expect people to voluntarily pay higher taxes than required, and that would be a ridiculous way of running a government.
It's stupid to say they are "not paying their taxes", because in fact, as a policy, our government has chosen not to tax them. If people disagree with that policy, they should focus their ire on government, not on billionaires.