In the 1960s, George Romney, Mitt’s father, regularly turned down his bonuses from his auto executive job, perhaps in part because his marginal tax rate would have been about 90 percent

If this is true he’s a fucking idiot. 10% of $x is better than $0. More likely the reason was that the bonuses pushed him over some threshold so he lost some other benefit, making it a net loss, or he negotiated some alternative compensation mechanism that had reduced or deferrable tax liability.