Politicians are too risk adverse to approve something that might turn out to be a waste of money. Organizations like these oftentimes even work with government on some level doing stuff government isn't really able to do for various reasons. And 10 billion is a drop in the bucket for the US government.
I think in the long run it tends to work out better. You're focusing on a single issue I might disagree with. I'm looking at all issues this can affect - those I agree with, those I disagree with, and those that everyone agrees with but doesn't really give enough of a crap about so they don't push to have their governments allocate a budget for it.
Looking at just rabidly disagree/agree is a very thin slice of things opposing this sort of action affects.
So to answer your question, yeah, I wouldn't oppose it for an issue I disagree with, because even if they exist I think the system as a whole nets out towards the positive end of things.
This view is mostly true if you agree with that thing being a problem. What if the billionaire unilaterally decides to spend 10B to combat the pro-choice/pro-life movement (whichere you agree with)?