Maximizing Moral Virtue

[Belacqua]

The important difference is that the first picture represents a developing human body with no capacity for suffering and no conscious awareness.  The second is a young human being with a name who has bonded with other people, cries when it's scared (because it can process and form ideas about its environment), and is busy formulating a network of ideas about the things it interacts with.

Yes, I think your opinion is one that many people hold. 

In your view (as I understand it), there is some kind of ontological change (from non-human to human, from non-murderable to murderable) when the thing in question develops the ability to suffer and have conscious awareness. 

You don't really give a reason why this is so. Nor do you give a fair account of the reasons why many people who disagree with you (e.g. Aristotelians or Thomists) think that the ontological change occurs earlier. 

The second photo shows something adorable, and the first doesn't. But, as you say, it would not be a good argument to rely on people's instinctive responses to the differences in appearance.