As someone who really, really, really dislikes kids, I can see why choosing the life of some unnamed brat over that of one of the beautiful creatures you know and work with each day would be difficult for some.
Maybe I'm a bad person because of it, but hey, we've all got our priorities.
Of course it would be difficult.
It was also the right thing to do.
If their response of the zoo had been " that kid, the parents are dumbs," and people were largely ok with that, it would signal our culture had gone to a very dark place in terms of respect for human dignity. This isn't just about whether a human life is more valued than a gorilla, but which people are valued and which aren't.