> the vast majority of people, lacking meaningful capital, can only secure income by selling their time and labor

It's just time and it's the only things humans value. The only way to provide value for another person is to use your time to do something faster than they could do it with their time. That's it. There is no other way to secure income outside of inheritance or charity which is just receiving something of value without giving something of value. There's a reason why most of the income goes to older people, because the younger people haven't accumulated that much time to exchange for money. The nice thing about time is that everyone earns it at the same rate, 1 second per second.

Capital can be a lot of things, not just machines and property. Any experience you have is capital, any training is capital, any education is capital. Capital is anything makes accomplishing things take less time.

The difference between socialism and capitalism is the idea that one person's time can have different value. That's really it.