rich pay for the welfare of the poor because rich enjoy influence which they do not acquire through effort but simply inherit just because they are rich. its like im the first one to climb the stairs which gives me the ability to partially stop others from coming up just because i can due to my being at the top.
secondly, many people are born rich which allows them to acquire better education, lyf style, and consequently jobs. it wasnt their right to be been born rich just how the child in a poor household did not choose poverty before coming to this world..
and thirdly, value of a good is not only determined by one's effort (or labour, as Marx suggested) but it also includes the value of resources made available to mankind by God. Thus, part of the wealth is due to the resources for which no one paid. And it is by this right, God orders the rich to share their wealth with the poor - as mentioned in the three major religions (and all others as far as i know). Because the wealth of the rich and the poverty of the poor is not solely because of their individual actions.
now if the rich are left on their own and poor are left on their own, with the government sitting and being deluded by the arguments of the trickle down economics, distribution of income (inequality) will keep becoming more and more skewed and ultimately ur society will collapse with every class becoming an enemy of the other class. the consequences of any sort of injustice can only be delayed but not completely diffused.