The issue is that in the past, if the parents were bad, then the kids would just die (and the parents probably wouldn't live that long either), and so the problem would take care of itself. But now things have improved just enough that death isn't an issue, so we're stuck with all these people who (according to the natural state of things) should have died.
Now you can debate all you want about whether these people have the right to live or not, but the fact of the matter is that their existence creates a new downward drag on society that did not exist before, and they threaten to bring down the rest of us if we don't do something about it.
Now you can debate all you want about whether these people have the right to live or not, but the fact of the matter is that their existence creates a new downward drag on society that did not exist before, and they threaten to bring down the rest of us if we don't do something about it.