People who contribute more to society are entitled to a better standard of living afforded by that society than those who don't contribute.
A few major issues here: 1) Contribution to society based on what rules? Increasing GDP? Where did anyone sign up for that or agree it was a social goal? Is it written somewhere? How are we really going to define this? We can identify lots of economic activity that is directly harmful to society, would these people be penalized and subject to even lower standard of living than loafers who do nothing?
Secondly hard work is great and will tip the balance, but we do not have a society that rewards based on merit (hard work). So long as power is structured with dynasty and wealth we will never have it. So in practice, this really turns into an argument that is proportionate to someone's level of disadvantage. Hey poor people: work hard, but neglect the nepotism, cronyism, corruption, and loafing of everyone above* you. *Where "above" often means experience, age, aggression, unethical, etc, in addition to power and wealth. Basically it seems you want to only hold disadvantaged people accountable for their work ethic.
what entitles them to a life better than poverty?
The same thing that entitles you to a better life through hard work: Nothing.
Thus spake the master programmer: "After three days without programming, life becomes meaningless." -- Geoffrey James, "The Tao of Programming"