I don't pretend to know how "people are by nature". Perhaps they are greedy and selfish, perhaps not. In any case, the concentration of power in the hand of few people increases the systemic risk that bad characters (greedy and selfish people) do great harm to society. That's why socialism is a very bad idea.

You write that capitalism has killed people? No, capitalism gives people the possibility to deal with other people, to get a job, to buy bread, to go to a doctor, all these little actions necessary to survive. If these deal are not allowed, you live in North Korea.
Capitalism is not a system, it's just the sum of actions that people do if they are allowed to provide for their livelihood.
Communism, on the other hand, is a system run by politicians that either kill directly millions of people or - due to their ineffective and inefficient system - let their people starve.