You are arguing a point of semantics: the butterfly starts off life as an egg that has been fertilised within an adult female's body. There is then a process of enveloping the embryo in a protective casing in which the foetus will develop and ejecting it as an egg. Only when the foetus reaches a point at which it is independent of the food source within the egg, does the caterpillar appear. This is "the moment of birth."
Thus, as we have the parasitic development of the foetus within the mother’s body to be followed by a period of parasitic feeding on milk, in the butterfly, the foetal stage starts in the body of the adult female, but continues to the parasitic feeding in the egg which is exterior.
A living creature, comparable of independent existence appears in both cases. With the caterpillar, the independence is immediate whereas, with a baby, it is probably about 9 or 10 years. However, the time taken for exterior development is an irrelevant consideration, so the caterpillar, pupae, butterfly parts are also irrelevant.
To perform an abortion on a butterfly, you would either have to remove a developing egg or squash the egg that is now outside the adult’s body.