The trope that a successful businessperson should "give back" as if they've taken something is an evil perversion of the American economic system and of capitalism itself.
A thief? A country that worked hard to give him a chance at his dreams of success - are you kidding? It worked just as hard for you - why don't you pay a few hundred million dollars in taxes, as Saverin will? The "country" didn't work any harder for him than it did for you.
Facebook created billions of dollars of wealth - $96 billion or so - out of nothing, and created thousands of jobs and far greater pleasure and wealth and utility for its millions of users and customers and affiliates. Facebook and its founders have no need to "give back" - they've already done the giving with their great ideas and brilliant execution, and $96 billion is very precisely a measure of how much they've given.
You mention all that infrastructure - but that infrastructure was not bought with income or capital gains taxes. Gasoline excise taxes pay for the roads (except when they're looted for blackhole "green" projects). Airports are funded by airlines and concessions and gate fees. The mail system is mostly paid for by user fees, and should be entirely so. Public education is paid for by property taxes which have nothing to do with Saverin.
Don't confuse taxes with social good. Warren Buffett and indeed Mark Zuckerberg (if not Steve Jobs) are giving large pieces of their fortunes to charities not because they want to "give back", but because charitable gifts allow them to decide how to spend it, and allow them to keep politicians from squandering it.
You happen to mention fire departments. Not too long ago, fire departments were funded by insurance companies or by annual subscription. And in those days, the local fire chief didn't make $250,000/year (as one nearby chief does) or get $700,000 annual pensions (as another does).