This is a linkpost for http://plato.stanford.edu/entries/nonidentity-problem/#WroLif
Here's another case of non-identity, which deserves more attention: having a child. This one's not even hypothetical. There is always a chance to conceive a child with some horrible birth defect that results in suffering followed by death, a life worse than nothing. But there is a far greater chance of having a child with a very good life. The latter chance morally outweighs the former.