The thing is, as IAmACat rightly said earlier, it's about equality of opportunity, and that is not only being eroded, but accelerated in its erosion.
This will, I'm afraid be a generalisation, and of course there will be exceptions to this, but...Those who are the children of bankers/CEO's/fund managers/lawyers get a better education, with a stronger focus on pastoral care, which makes them more polished at university and job interviews. Such children generally don't need to get Saturday jobs for spends, so are more able to do the extra curricular DofE awards, youth parliament, debating society, charity missions etc., which help with university/job applications. Then if they want to get into the plum professions (banking/law and so on) Mum and Dad have connections, and get them work experience (or unpaid internships, see above re Saturday jobs), and they are therefore more likely to get into what are very competitive industries if you try to do it on talent alone. I have seen this, professionally, for years!
Now, that might seem like I'm bashing these kids, which I'm not, I would, after all, get or use any advantage for my own children (without treading on someone else to get it I hope), but when the parents of these kids suck as much money as possible out of the system, whilst depressing wages for those under them (and don't kid yourselves that investment bankers and fund managers don't do this by putting pressure on CEOs to reduce costs) then it's hard not to feel some anger.
Philip Green may be a very nice person, but he sends all his money offshore, pays non Dom tax, and a generous corporation tax rate in the UK, and I suspect there are a fair few BHS workers who receive tax credits to top up to a living wage (no disrespect intended to any retail workers, BHS or otherwise). That is what makes, imo, people cross about high earners. There is nothing wrong with earning a high wage, there is something morally a little whiffy about earning a high wage, then complaining about paying your due tax, and thinking those who have so much less should put up with an ever decreasing share. And I say that as a higher rate tax payer!