Not everyone can pull their weight. Someone out there is a mentally handicapped quadriplegic. You’re simply not going to get a lot of value out of him.
So why keep that person around? We fear death, but that doesn’t make death “bad”. Needless suffering and pain is bad, but we can kill people painlessly (or could, if it weren’t for bans) so that’s not a component. The loss of a person is a loss of the possibility that that person represented. Except, in this case, that’s not an issue because the person has no possibilities. His death might present a loss to those around him, and cause them to suffer. But maybe they’d be just as happy to not have the burden or, more probably, they might have a better and easier life overall at the cost of temporary suffering. Or lastly, because he is a person and he did not so choose it and we have no right to force death on him. Except, the right to choose ones own life is based on the assumption that all mankind was created equal. Factually, we aren’t born equal. Nor are we equal through all stages of our life, hence why children are treated somewhat like property, why a child can’t give consent, why someone who will be horribly ill or mentally incapacitated can give their medical choices over to someone else.
Really the only argument in favor of keeping around someone who is a drag on society and a drag on those in his immediate circle (e.g., his family), is because we have the spare resources to allow for it and it prevents us from having to make the hard call.
But do we actually have “spare resources”? If a useless person is a drag on his family, preventing (for example) his sister from ever getting that degree she always wanted, going into chemistry like she wanted, and discovering a way to allow us to cheaply separate hydrogen off other compounds, that’s a great loss to society. All of the money and food that society and our taxes provide to this useless person could have been routed to someone in a developing country, who wanted to better his state and the state of his country, so that fewer people were in need. Money and food go a lot further in a developing nation than they do in the US. All of the “spare resources” that are going to support a person who is a drag on society is a “spare resource” that isn’t going to someone who would be pushing society.
Really, the only reason to have a useless person around is to satisfy a certain view of morality. Morality changes over time, because we learn more, think about things more, and try to work our precepts back into axioms. Some things just aren’t going to become axiomatic, because they just aren’t always true.