It should be obvious, but taxing consumption disproportionately affects low-income people who are the least able to afford it. Conversely, as the sister comment

It should be obvious, but taxing consumption disproportionately affects low-income people who are the least able to afford it. Conversely, as the sister comment alludes to, if a person has less money, they are far more likely to spend the money that they save from tax breaks. See also: the declining marginal utility of money.