Unnerved means the parents are not sure what they have and the may kill it. How would you feel knowing you gave birth to something new? Your instincts would tell you to destroy it.
Do you not have the phrase
'a face only a mother could love' in the States?
Or to put it in more real world terms - there is a bird in the Old World called the cuckoo which lays their eggs in the nests of birds of other species. When the cuckoo chick (which looks nothing like the young of the species that owns the nest) hatches it is fed by the 'adoptive' parents - even after it has thrown all the natural chicks out of the nest.
So based on an actual example from the natural world your claim about the parents being unnerved and killing it is on very shaky ground.
I wish I didn't know now what I didn't know then
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