Its easy to throw numbers like that around if one wants to feel sorry for yourself, its like the old joke though that's punch line ends with "its only you and me doing all the work, and you're reading the internet right now!"
If we're talking about income taxes, when one thinks about it, yes, 40% of the people paying all the income taxes is about right. Approximately 20% of the population are under age to tax, and about 20% of the population is retired. With that bottom twenty percent, well you people who have kids can thank those of us who didn't have kids for supporting them all those years. You're welcome. But I digress. So of the remaining 60% a third of those aren't paying taxes of the income sort. The bottom bunch, the poor, don't earn much money, but in the big scheme of things don't cost much money. However part of that working age non tax paying bunch are people who manage to avoid taxes - they don't earn a traditional income like the rest of us. Unfortunately our government likes to protect those people's ability to not pay taxes, since once you get that much money you can buy a lot of political influence.
Arguably if you are in the top income tax bracket you're probably paying too much tax, however if you are in the top 2% of income earners, it probably means you aren't in the top 2% of wealthy people. Think about why Warren Buffet's secretary pays more taxes than he does.
When it comes to "fair share" one should remember that one should pay proportionate to how one benefits. For an aviation tie in, when it comes to say, paying for ATC, should the regular pleb pay for most of it, who maybe can afford one or two flights a year, or should the guy who can zip around on a private jet every day pay for more of it?
