Because they're on the receiving end of the stolen property.
Let them carry the load too and then more will care how heavy it becomes.
That isn't exactly how it works. Regardless of the tax structure, some people are net tax consumers, and some people are net tax producers. Welfare recipients will continue to be net consumers, and will still want taxes increased--after all a few pennies at the checkout lane from them, adds up to thousands more dollars per year to them. Likewise government contractors of every description.
While I'd like to see the "freeloaders" eliminated, as you're saying, I point out that the real "freeloaders" include some people who pay very high income taxes. Kennedy pays income tax--but he is still a net consumer of tax dollars, and would still favor raising taxes for that reason. Likewise any net consumer, form the lowliest welfare queen to the highest-paid CEO defense contractor.