There’s nothing magical about exceeding a 50% marginal tax rate. (Hitting 100%, sure, that would be bad.)
There’s definitely a psychological threshold there for most people. I ran an informal survey a few years back about what tax rates people would consider fair, and there was a very strong clustering at 50%.
I have a hard time understanding it myself. The whole point of taxation is redistribution, so why would you care whether you’re “winning” versus the marginal tax rate?