[Semiapies]

"near to 100% of input kids are neglected or abused"

Untrue. Children end up in the foster care system for a variety of reasons, including simple loss of parents or a woman (or teenage girl) knowing she can't care for a child.

"significantly lower proportion of those kids neglected or abused"

The evidence is not as clear on this as you'd like it to be.

To correct your example, if we had a drug that caused strokes or death in a significant percentage of cases, simply saying, "Well, many of the patients we'd give it to would otherwise suffer strokes or death," would be a quick route to an FDA rejection.