They pay close to it and it's a heck of a lot closer to 50% than the folks who don't pay any tax on their income at all.
I just checked. Millionaires have about $11.4 trillion in income this past year. That means a 1% increase in "fair share" would be what....$11.4 billion? That's a pittance in terms of Federal spending. (Of course the argument can be made that I'm talking taxes for all levels but talking only Federal expenditures.) Suppose the rate was adjusted so that they paid 10% more. That's still only $114 billion. How much? give us a number. Rather than just waving your hands around, tell us how much is a "fair share"?
The millionaire in the US is somewhat an endangered species. The number here declined about 125,000 while the number world-wide grew by 175,000.