Besides the moral standpoint, I am fairly convinced by the practical argument that redistributive policies make the economy work better anyway, from the data I have seen.
Poorer households spend a much higher proportion of their income on consumption than rich people do. There is a fairly robust practical argument for things like unemployment benefits and subsidised/free necessities as the overall effect is to free up some of the low-income household budget for spending on crap like widescreen tellies (and Cath Kidston wellies) and thus boost consumer demand in the economy. This is why I (personally) think extreme supply-side economics is short-termist in that it is basically stripping the ability of poorer households to consume out of the economy.