The legalized expropriation of income (i.e., taxes) is morally dubious. Anti-tax movements have sprung all over the world and their philosophy permeates the ideology of political parties in many countries, not least the USA. Taxes are punitive: they penalize enterprise, success, entrepreneurship, foresight, and risk assumption.
Welfare, on the other hand, rewards dependence and parasitism.
According to Rawles' Difference Principle, all tenets of justice are either redistributive or retributive. This ignores non-economic activities and human inherent variance.
Moreover, conflict and inequality are the engines of growth and innovation - which mostly benefit the least advantaged in the long run. Experience shows that unmitigated equality results in atrophy, corruption and stagnation. Thermodynamics teaches us that life and motion are engendered by an irregular distribution of energy. Entropy - an even distribution of energy - equals death and stasis.
What about the disadvantaged and challenged - the mentally retarded, the mentally insane, the paralyzed, the chronically ill? For that matter, what about the less talented, less skilled, less daring? Dworkin (1981) proposed a compensation scheme. He suggested a model of fair distribution in which every person is given the same purchasing power and uses it to bid, in a fair auction, for resources that best fit that person's life plan, goals and preferences.
Having thus acquired these resources, we are then permitted to use them as we see fit. Obviously, we end up with disparate economic results. But we cannot complain - we were given the same purchasing power and the freedom to bid for a bundle of our choice.
Dworkin assumes that prior to the hypothetical auction, people are unaware of their own natural endowments but are willing and able to insure against being naturally disadvantaged. Their payments create an insurance pool to compensate the less fortunate for their misfortune.
This, of course, is highly unrealistic. We are usually very much aware of natural endowments and liabilities - both ours and others'. Therefore, the demand for such insurance is not universal, nor uniform. Some of us badly need and want it - others not at all. It is morally acceptable to let willing buyers and sellers to trade in such coverage (e.g., by offering charity or alms) - but may be immoral to make it compulsory.
Most of the modern welfare programs are involuntary Dworkin schemes. Worse yet, they often measure differences in natural endowments arbitrarily, compensate for lack of acquired skills, and discriminate between types of endowments in accordance with cultural biases and fads.
Libertarians limit themselves to ensuring a level playing field of just exchanges, where just actions always result in just outcomes. Justice is not dependent on a particular distribution pattern, whether as a starting point, or as an outcome. Robert Nozick "Entitlement Theory" proposed in 1974 is based on this approach.