In a capitalist world, it can be hard to remember this. But despite what you are pressured to think, your value as a person does not come through what material value you create for others.
If their illness is to a degree that they’re completely disabled then that’s an exception. Under those situations I think their community should provide what is needed for that person so that they’re comfortable for whatever duration remains in their life.
Just to go a bit deeper, would you tell your own disabled child that they are a drain on society? Would you think highly of others who told them that? I’m willing to bet in those circumstances your views would change, so why not reconsider them now?
Laughter is a social good, even if it makes no money. Practicing compassion is a social good. Receiving compassion is a social good. Disabled people are capable of all of these and much more. You are free to believe as you wish, but as someone who has lived on both sides of this issue, I don’t believe your views will sustain themselves under the scrutiny of experience, should that experience ever find you.