But this "survival of the fittest" is just a strawman. The market is collaboration, absence of violence.
But there is no economic incentive for the strong to help the weak. Presumably morals would play that role in an anarchist society but it is a very real problem that can't be ignored.
Leaving aside the fact that there are motivations for action besides economics; there are economic incentives to help others both weak and strong.
There are very few people who are really helpless anyway. If it wasn't illegal to hire people, build things, and grow things people very few people would have trouble making their own living. For those that cannot, we know there are lots of people who care about them since this is the most common argument I hear for the state "But I want a state because I care about the poor" See lots of people care. People who care about things do them. Even in our society with it's billion dollar aid programs and 50% taxes on people with excess resources there are thousands of charities getting well funded.
I could not have answered better.
The first reaction of an authoritarian is always: "but what about the poor?" like if they really care for the poor and not for power.