Socialism is good precisely because humans ARE selfish in nature. If no one was interested in hoarding money, owning others, dominating people financially, or carving out vast fortunes, then Capitalism would be the perfect economic system. Efficient, fair.
But it's not.
Capitalism is dominated by greed, with the moral that greed is good. The Businessman is held as a standard, and his greed is praised. That greed is a light to society, and the rewards of capitalism are dangled like cheese, to force rats to run through a maze against each other.
Socialism is the alternative. It's not new either, as the problems of capitalism became readily apparent mere decades after the system became industrialized. Now what is Socialism? Simply put, it is when the state owns the means of production, when the state owns capital. The state administers industry, and provides equally to citizens, who no longer have to work dangerous jobs for minimum wages. They can be assigned a living wage, or merely provided with everything they need.
So Socialism IS good BECAUSE humans are selfish in nature. And, from a Marxist perspective, Socialism is the forerunner to Communism. The goal is that through centuries in a society without money or class distinction, humanity will slowly look on greed as an ancient emotion, something backwards, and the new values of equality will be dominant.
Whether or not we ever achieve that state is debatable, but the societal wisdom of Socialism is undeniable.
Socialism would definitely be good if we imagine that humans aren't selfish. The root idea of socialism is significantly good and well-structured. The reason why it fails to be good is because of selfish human nature. We always want more. We never get enough. Real socialism should have leaders, but not dictators like in North Korea, as an example. It would be an amazing form of government, where the government itself works for people(society).
If socialism worked as intended, it would be great! The idea of socialism only fails because humans are selfish in nature. If there's an opportunity for power, we want it (hence the tyrannical past of socialism). Other's work would make it so we don't have to, and because we're all human, no-one else works either. Fear of death is the only thing that keeps socialism afloat among citizens. True socialism wouldn't have a ruler/rulers, other than all of the people together. In the past, all socialism was tyranny, rather than true socialism.
People fuss over "capitalism" and "socialism" but the best solution is not always just capitalist or just socialist. And furthermore, a solution that is government-run may sometimes be best but where it isn't promoting more "equality". Society needs to be thought of as an organism and then we do what is best for that organism not limited to or boxed into categories of "capitalism" or "socialism".
If people weren't selfish in nature then anarchy would make more sense than socialism. Nobody ever hurts anybody else even if it would personally benefit themselves ever and if people who get into disagreements were always as peaceful and patient that they could sort it out themselves then anarchy would work fine. But as it is that's not the case. It's actually because of human selfishness that sometimes the government has to step in. But also because of human selfishness that sometimes the government's power has to be reigned in.
The redistribution of material wealth is never justified. Socialism creates a system where those who are unable to support themselves feed off of the able in a parasitic relationship. This engenders only feelings of hatred and fear toward your fellow men. Also, your question is not asked in reality. People are selfish by nature because this is the only way man can properly survive. The argument must first be made that man should not be selfish.
Socialism, even in an ideal world, would not would not be fair. What is the point of working harder than other people and gathering more resources in turn if that is all divvied out equally? The incentive to gather resources is a major factor in the wellbeing of everyone, because as a product or service becomes more valuable at lower prices, thanks to capitalistic thinking and capitalistic "greediness," other humans also benefit. Remove this incentive, and humans would not be as prosperous. Advancements would occur, but at slower rates. Additionally, Socialism is not fair to those individuals who work harder and study longer or practice harder or refine their practices or intellect, and to not reap the benefits of that investment.
Socialism can only be useless or immoral. It is oxymoronic to force people to do what they are willing to do. The very fact that you must pass positive laws (laws declaring a duty) means someone does not wish to do it, and the purpose of that law is to force the dissenters to submit.
It is immoral to force duties on people who did not previously consent to them.
If people were perfect we wouldn't need socialism. And as people are not perfect we always end up with greedy abusive tyrants violently enforcing their corrupt version of socialism.
So socialism is either a foray into how abusive government can get or utterly unnecessary depending on how greedy or good people are.
Even if humans weren't selfish, socialism would not be a good or fair system. The idea of socialism is that everyone is equal so everyone should be rewarded equally.
However, if someone with determination who always tried his best at his job got paid the same amount as someone who constantly slacked off, would that be fair? No.
Socialism makes it pointless to work hard, as everyone is paid the same amount, in the end. No one would bother to invent new things or contribute ideas, because they might as well just relax - they'd not get paid any less for not working well.