The problem is that it perpetuates the myth that private charities are a more worthy recipient of money than government. Most of these people have avoided giving their fair share of taxes to the government their whole lives, and now they are giving gobs of it to charities.
That's not really what we need. It would have been more beneficial for longer if they had simply worked to get the high income tax rate raised.
The things that America really needs more of are basic government services. We need money for schools and teachers, we need money for the homeless and unemployment, we need money for prisoner rehabilitation and drug programs, we need money for libraries and roads.
What we don't really need is more money for "alternative education" and laptops for schools and "measurement based learning evaluation" and all that marginal shit that the Bill Gates foundation does.