By his medical science's logic, he was once a parasite on his mother...
Fixed that for you. Technically speaking, every fetus is a direct physical parasite until birth, and most of them remain indirect non-productive resource parasites on their parents for another 16-24 years thereafter.
The fetus takes energy from the mother, often at a dire cost to the mother, and gives nothing in return. The mother's body is biologically programmed to supply the fetus first, herself second. Sure, it can be argued that it brings an emotional prize, but only if it is a wanted child. The comparison is more apparent when a woman who does not want a child is being "forced" by the state to carry it. The fetus has a parasitic relationship with the mother, living off her body often at an extreme cost to the mother in terms of nutrition, health, and in some cases, to her very life. Before modern medical science (when religion dominated culture), death during childbirth was not all that uncommon.
These are indisputable medical facts. Deal with it, theists.
Cancer also has a right to life.
Every major metropolis is a cancer of this planet, if you adopt nature's perspective. So what?
It's evolution, baby! We live in an indifferent universe, folks. It cares nothing for our fates, cares nothing for the fate of our entire backwater little solar system. Tomorrow every living thing in our entire galaxy could be sucked into a black hole, and the universe would just keep on ticking away like an eternal clock. I shouldn't have to tell anyone this, it's all self-evident truth that is being desperately denied by theists with hideous mental gymnastics. You may be wondering why it's so important to me that you all understand this. It's because modern humanity is a God pretending that it is only a child, and that is extremely self-and-other-destructive behavior.
Recognizing our responsibility as the sole Stewards of Earth as soon as possible is paramount to our long-term survival as a species, and
it may already be too late.
P.S.
The difference between an
unwanted fetus (womb parasite) and a
human being is that a human being has a set of deep-rooted human relationships - human beings have people that love them, people that will mourn their loss. Fetal parasites unwanted by their parents do not.
P.P.S.
I agree that abortions should never be anyone's
goal, and will disclose that I myself (under 30, no children) have a vasectomy so that no women I lay with will ever have to face such a terrible choice.