One of the reasons I think that chart has significantly gone toward people believing the upper income should be more heavily taxed is government interference/safety nets. Human nature, being what it is, if one is receiving something for nothing (or little to nothing), one is going to want to hold on to it. This is why I am a big proponent of work requirements for any government assistance - I read somewhere (and don't have time to look it up now) that work requirements for Medicaid reduces participation. Anything that requires some work instead of none, some people are going to decide that it's not worth it to work.
Because of this government "help" and the way in which one loses it if one's income reaches a certain level, no one is incentivized to earn more lest they lose their benefits. And of course, the more people on welfare and who have less, the more they look to those who have to tax them and continue getting this government "help". I think that explains why over time (the recent decades), more and more of this thinking has become prevalent. Imo, it is the explosion of the welfare state that is the cause of people NOT trying to better themselves financially and actively seeking to stay under a certain income - part of the reason why I hate Obamacare and its insiduousness regarding Medicaid (able-bodied people under a certain income getting free healthcare with no work requirements - although Trump administration is trying to change that - I'm sure the first lawsuit is ready when it gets implemented).
Money earned from capital gains is not taxed with SS and Medicare as is earned income - you get to keep more of it. So, it is much more profitable to make money investing your money than through labor - and this is what the top x%ers do and those who earn only enough to pay living expenses can't. Most of you scoff at me and think I'm crazy when I day trade bit coin. How do you think we survived on one income all these years? Yes, I took a lot of risk - some I win and some I lose but overall, it's on the win side. And because I took such risk with my money, I should be allowed to keep it - not have it taken and re-distributed to some one who has done nothing and taken no risk. On that chart, as income rises, more people think that they (or others) should not be taxed more. Now, if you do not feel the same way, please feel free to give away what you have but keep your hands off mine. Many of you are young now, but as you earn more, your thoughts on this matter may change.
AaronY, please don't fool yourself into thinking that the man holding the bag of money only applies to Republicans - just like the sexual scandal that crosses party lines, both sides have stacked the deck with their law-making/policies (or been donor to) - Democrats too don't care a rat's behind about the little man - these policies are all to gain voters in order to stay in power and enrich themselves (see the immigration mess).