OP never said low income workers contribute more than high income workers, so that's a battle that doesn't need fighting. She said they contribute more than they take. No need for higher earners to be defensive. If you pay higher rate tax you almost certainly contribute a lot more than I do in net terms (I've never earned much over £30k and currently earn a fair bit less), but that doesn't mean you're subsidising me. I no longer get child benefit etc as my DC are grown and three of them are currently paying a decent whack of tax themselves.
With the examples given above like healthcare workers, carers, bin men etc you can argue they provide societal rather than monetary value - well, than direct monetary value anyway; keeping the nation clean and healthy has an important knock-on effect on the economy as well as quality of life in general. But what about, say, manufacturers? The people paid least must, logically, earn more than they are paid. The excess value of their labour has to cover their own wages, running costs, distribution costs, salaries of professional staff above them in the chain, and shareholders' dividends. If it didn't there would be no company and no-one would be earning anything. The entrepreneur makes it happen, and more power to his/her elbow, the sales team turn the goods into income, the accountants keep it legal and profitable, and so on, but without basic labour it wouldn't happen either. Without the excess created on the shop floor the professional staff, accountants, sales people, directors, wouldn't have that decent income to pay their high taxes which are then snaffled by government to, among other things, pay tax credits to their own shop floor workers. Go figure. Tax also goes to create the infrastructure that makes manufacturing viable, educate the next generation of workers, keep everyone healthy enough to work... it's a big churn of resources and everyone in that scenario is putting in their bit. Some are paying more taxes whilst others may be paying no taxes at all, but between them they're turning a profit for the company, and by extension the economy, as a whole.
Pay differentials should reflect the relative skill and responsibility of the role but seem to have got massively out of hand in recent years. We don't all need or deserve a mansion or a fleet of Ferraris, but something is wrong if you work full time doing a useful job yet still can't afford a roof over your head without the government chipping in. That's why the minimum wage is a necessity and housing costs really should be controlled some way or another. I blame the reduction in social housing provision at least in part, but admit I'm no expert.