What you're really asking is why we should have progressive taxation.
First, you just helped to explain part of the reason. A percentage of every household budget is spent on price inelastic commodities. That percentage to income ratio is clearly higher as income is lower. Therefore, removing income from the poor and working class detracts from necessities whose demand by those classes will not change. In other words, they will still require those items.
Second, vertical equity. Higher incomes have higher percentages of disposable income which means that they are in a position to afford more money spent on the public.
Third, the wealthier classes receive more benefits from Government spending in terms of defense and infrastructure than do the poorer classes.
Fourth, Adam Smith and Karl Marx both agreed that taxes should be based on proportion to income. Supply-side economics and benefits for the wealthy came later from the likes of bogus economists like Laffer and Friedman. It has never been found to achieve anything more than very high income disparity and stagnant wages. Note that most economists do not support the views of Friedman or Laffer. Most support redistribution:
LinkFifth, the law of diminishing marginal returns.