The president is of course welcome to donate as much of his extra money as he likes to the federal treasury. He knows Timothy Geithner personally and can probably get a guarantee that his check will be cashed without delay. And since the president is so ready to impute unpleasant motives (like greed) to those who oppose tax increases, perhaps we should impute some sort of moral failing to him for not having thus far contributed his spare change to the government.
I can think of many excellent reasons to oppose higher taxes that have nothing to do with greed.
The government is a spigot. Just when you think that spending has passed some sort of gasp-inducing peak, it blows right past it. Some of us thought the half-trillion-dollar deficit at the end of the Bush administration was vertigo-inducing. In just the past two years, President Obama and the Democrats have tripled the deficit and added $3 trillion to the national debt. This added spending, 40 percent of which was borrowed, was advertised as required to create thousands of jobs, kick start an economic recovery, promote "green" energy, "save" thousands of jobs that would otherwise have disappeared and provide long-term unemployment insurance for those out of work.
The stimulus bill succeeded only in the last goal. (Slogan suggestion to the Republican 2012 presidential candidate: "If you want an unemployment check, vote for Obama. If you want a job, vote for ___.")
Arguably, raising taxes to cover this incredibly brainless and wasteful splurge encourages irresponsibility on the part of decision makers. A refusal to raise taxes will force office holders to prioritize spending.
The president may be perfectly confident that the best use of his excess cash is to pay more taxes. Those who live in the real world may consider the government hopelessly wasteful and inefficient. If the president really wants to get the most bang for his charity buck, he'd be far better advised to donate to the Boys and Girls Clubs of America or the Wounded Warriors Fund than to the IRS.