First of all, everything collectively known about humanity shows our ancestors were largely not violent primitives, but instead they experimented with a wide array of different socials structures for millenia. Not all of them perfect, but violence wasn't a "daily way of life".
But sure socialism won't magically make violence, psychopathy, or bad actors disappear. It won't necessarily bring people closer together. The point is largely about who owns the means of production. But there are also absolutely forms that encourage and reward cooperation in stark contrast to what we have under capitalism.
In fact capitalism loves cooperation. They love monopolies and consolidation because they thrive under internal cooperation. Any attempts to the contrary have failed hilariously.
Cooperation is absolutely, and without doubt, one of humanity's greatest strengths. It baffles me you're trying to argue otherwise. In our current capitalist society, with how isolated we are, it may seem beneficial not to cooperate at another's expense for the immediate advantages it brings you. But its short sighted, in the long term cooperation benefits more people, and it always has.
In the right social structure this would be rewarded and encouraged, and most everyone would be better for it. History shows it, game theory shows it, life on earth shows it, cooperative enterprises show it, and even internally capitalist enterprises show it (but who benefits?)