Donating 2.5% means that you get poorer and poorer over time unless you can make more than that per year back. 2.5% of wealth also means non-liquid assets such as house, how do you donate that? Get credit?
If you are middle class and your house etc is eg 1M$ net worth you are giving 25k$ per year. At 0.5M net worth its 12.5k$ per year.
2) You assume that those people would know how to handle that money well. We see what many poor people do with money: buy trash like soda with food stamps that makes them even more ill and causes them more financial burden due to poor health.
Are you sure that money would be well spent, or is it better to invest in better technology that will benefit everyone?
3) Why would hard working responsible middle class people give their money to those that buy cola with it? Mass revolt, people care about their families only.