Why do U.S. corporations face a peak marginal corporate tax rate of 40% when the global average is 23.6%? Is this fair? Should it change?

Because unlike countries in Europe, US marginal tax rates aren't what Americans pay. They are the most Americans will pay. But since just about no one pays the max, the top marginal rate is basically meaningless.

In reality, US corporations usually pay much less than the 40% rate thanks to a litany of exemptions, subsidies and loopholes. US corporate taxes are not wildly out of line with global norms (if at all). I don't think it's fair that different companies and industries pay radically different rates. The US tax code is overflowing with exemptions and deductions and loopholes that have accumulated over decades. Many of these were implemented for dubious reasons, like to serve a particular state or industry, or to encourage certain behaviors that may no longer make sense. I think all of that is bullshit. Scrap it all and start over. I think there should be some special exemptions - wind and solar come to mind - but Congress should carve those out from scratch to reflect the realities of today's economy, not holdovers from the 1970's. And they should have sunset provisions so they don't become permanent fixtures of a changing economy, and so the tax code doesn't once again become bloated and unwieldy. And yes, I think a lower overall corporate tax rate makes sense, once most loopholes and exemptions are removed. I would also like to see a small, special corporate tax solely to fund corporate oversight - something which is woefully underfunded. http://www.forbes.com/sites/janetnovack/2013/07/01/gao-big-companies-paid-a-12-6-federal-income-tax-rate/

In fact, that's the nominal rate.  The effective average tax rate for most U.S. corporations is much lower, and much closer to the global average.