Why wouldn't I veto everything except the give me back my money tax? Now, I'm not actually ridiculously selfish asshole that doesn't think of others or the long term consequences of my choices, but it's a prisoners dilemma, with everybody else in your country, and defecting gives you money back. Cynically I don't think that'll work.
It wouldn't be a "Give money to anyone you like" kind of choice, but "Allocate money to these departments." Funding that you assign to one category would have to come out of another. Think basic research is a waste? Allocate less to NSF and more to foreign aid, or to something else that you prefer. Don't want to fund welfare? Move the money to defense, and so forth.
Obviously still open to gaming and abuse, but it's not as if the current system isn't.
