Sitting on billions of dollars in stock in a publicly traded company isn't really all that different from having a swimming pool full of gold coins. The day-to-day functioning of that company is not going to be affected if the billionaire sells shares to pay taxes rather than giving the shares to their children. An initial investment in a company is virtuous but once you have billions keeping that money in the family isn't really virtuous given that the alternative is contributing to the society that made the initial investment possible.
Investing in companies is contributing to society. Government is not society. Investing in Walmart so that the rural poor have more access to affordable goods is virtuous. And a whole lot of the contributions to government are absolutely not. Like the money that goes to build bombs to kill people in Yemen, or the money that funds your local police department's efforts to suppress protests against their unaccountable violence.
