In addition, I consider charity to be very condescending. It makes recipient dependent, in terms of power relations, on donor. Many wealthy people use charity to rationalize their empire building, and that's a symptom of this power dynamics.
The exact same problems apply to the State apparatus; sure, you can kick out a few politicians, but public pressure can usually kick out a head of a charity organization as well. Changing the system itself, on the other hand, is extremely difficult. And people obviously use it for empire building.
The idea that the modern State is an accurate representation of the democratic consensus is, in my opinion, absurd. It is not, for better and worse. And at least the Bill & Melinda Gates Foundation is honest about who controls its resources.