You're not going to get anywhere when you talk to people like this. You keep dismissing the human nature argument without citing any evidence. Some of what they say makes sense. Like how someone without a job or some other kind of work like being a volunteer is an outsider who doesn't contribute to society and dosen't recieve much support from society.
The person you are arguing with is missing something though - and that's that capitalism is problematic because of human nature too. If humans weren't so greedy capitalism would be less problematic. Rather than human nature being something that only causes problems for socialism it's something that causes major issues with capitalism as capitalism doesn't align well with human nature. Heck maybe the actual solution is to remove humans from making economic decisions at all and have computers make them instead; or perhaps even aliens.