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There are many arguments whether a sotapanna has a perfect morality/sila or not. But let's base this topic on this Sutta:
With what four factors of a stream enterer is he endowed?
...Is endowed with virtues that are not broken, not defective, not spotted, consistent, not blemished, not enslaved, praised by the wise as conducive to concentration and desired by the noble ones He is endowed with these four factors of a stream enterer....Anguttara Nikaya 9.27
Now, for example, a deadly worm is in the stomach of a sotapanna's child. The only thing to help his child is to kill the worm otherwise his child will die. With his perfect morality, what would a sotapanna do, will a sotapanna (naturally) let his child die?