Everything you're saying is true, and yet, I think that relying mostly on this line of reasoning to justify poverty reduction leads to discounting the importance of supporting disabled people and old people. I think most people believe that just because you cannot work, doesn't mean you deserve a basic but dignified standard of living.
>reasoning to justify poverty reduction __leads to__
This is slippery slope argument.
You are essentially saying that using economic argument for taking care of poverty can be used to justify not taking care of poverty and we should not use it.
It's hard to connection between importance of supporting disabled and old and economic argument for reducing poverty. Reducing overall poverty is net positive also for disabled and elderly.
I thus think that you have succumbed into logical fallacy.
