This is a sort of terrible analogy, but I'm going for it anyway: I recently adopted a cat and feel extremely powerful positive emotional feelings for him just by virtue of being around him and caring for him all the time, not to mention that he is incredibly cute and loving. But I don't feel for him the way I would expect to feel for a biological child of mine. I imagine one's feelings about an adopted child might be similar at first.

more: I'm not sure if you are saying parental love is a good thing or not, or merely factually stating that it could potentially be absent in an adoption scenario, but for the sake of conversation let's say you (or some imaginary interlocutor) are suggesting there would be some net detriment to child-rearing if parental love is removed: I wonder if one couldn't make more rational and intelligent decisions in the absence of the potentially-clouding fog of parental love. Is it necessarily a good thing for an established adult to want to die so that a 1-month-old infant could survive (insert imaginary scenario here)? Is it a good thing that parents see their children, the object of their overwhelming parental love, less objectively and with profound biases due to that love? Etc. - there are many examples of the biasing effects of biological love.

It's an interesting topic I think... non-biased (or at least less-biased) child-rearing as a result of reduced instinctual biological parental love.