Again, you are making the presumption that she would have caused pain to the child or been a poor parent. While she might have been a poor parent or drug addict in the past, that doesn't preclude her from one day being a good person and a good mother. I have some firsthand knowledge, too, but that doesn't mean I can predict the future.
Still, it is a loss whenever any human dies. We don't know what that person's future would have been. It could have been good for society or bad. It is no less wrong to assume good, than it is to assume good things about someone who WAS good that died. There are plenty of good people that became rotten in their older ages. Yet, if someone young and successful dies we don't assume they would turn out that way. Just as how we shouldn't assume someone with past problems is always going to be a problem, or be bad for the people around them. It like assuming once a criminal always a criminal and refusing to give people another chance. Sure, they might turn out to be even worse than they were, but they also have a chance to turn out good.
This isn't hopeless optimism, either. Many people change for the better in middle and old age.
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