Thanks for writing this, Phoenix! It was thought provoking and I plan to read McKenzie’s article after. I have a couple thoughts.
(1) I don’t think comparing the chicken to the fetus is equal. Chickens are the “host” of the egg. The unborn do not have choice, the person carrying the child (or “host”) does. I see the egg and the unborn fetus as being parallel. Thoughts?
(2) I don’t think the “right to life” argument holds up on either side, it assumes life is “good,” and doesn’t take suffering into account.
I would say the reason not to kill the pig is consent. A pig is revoking consent to being factory farmed and slaughtered every time they express distress (to put it lightly).
I’m trying to formulate and write out my thoughts about your title question. I’ll post another comment in the morning.