I'm not saying people don't like their own...

...children better, on average. I'm saying that it's not *necessary* for people to be genetically invested in a child to become bonded with it. Our responses to children are more generalized than that, not to mention our responses to other human beings.

And the examples you give only prove that socialization is much more important than genetics. I'm sure you'll admit that there are plenty of examples of adoptive parents who are just as bonded to their adopted child, if not more so, than many biological parents. Human beings are flexible, and their biological mechanisms are often so general that they give a heavy role to culture.