For one thing, not all the kids will grow up to be just like their parents. Some of them will escape the depressing cycle of early single parenthood, inadequate education, lousy jobs, and poor self esteem. Some will make it through high school and college and become contributing members of society.
Even if they don't, though, I don't think we should judge a person by his or her station in society. People who are on the lower end of society - I don't really know how to describe them - even drug addicts, still have worth. They may be a drug addict with no productivity in life, but they are still someone's sibling, or child, or friend, and as such bring some pleasure into another human's life. They might not have a job, but they might have a great sense of humor and entertain their families at Sunday dinner, or have a good listening ear and bring comfort to another person.
But mostly, I don't mind taking care of babies who are destined for less than greatness simply because they are human beings, and I think every human being has some inherent worth. Humans are not just another animal. I can't explain exactly what makes them different from other animals, but something does, and we can never forget it. It's what makes us always take the loss of human life seriously. It's why we can never be flippant about decisions to remove life support. It's why every baby must be treated with dignity, regardless of whether they are perfectly formed or have severe defects like trisomy 18 or holoprosencephally. That doesn't mean we have to treat every baby born, even those with terrible birth defects, with heroic life support, but we have to take it seriously if we don't.
Ali, I know where you're coming from and don't mean to be hard on you in this post, but never for one minute do I think my efforts on behalf of any baby are futile.