Maybe you would also donate your billions to charity. Well, good luck earning them in the first place while playing fair.
The Gates Foundation is dedicated to "tactical philanthropy" which maximizes investment "leverage" by allying with existing commercial/political interests whenever possible, often with strings attached. Gates has stated clearly that he prioritizes programs that are revenue neutral -- that generate enough income to sustain themselves. While that's better than a stick in the eye, that's not exactly "giving your money away".
And in terms of atonement, exactly what remedial actions are sufficient to turn a gangster into a saint? Martin Shkreli and Al Capone would like to know.
This is not a new issue, see https://en.wikipedia.org/wiki/Robber_baron_(industrialist)