Anyway, the fetus theory I was referring to follows.
Itoi (creator) has already stated that Giygas's lines during the final battle are actually from a traumatic childhood experience where he walked into a movie in which a woman was being raped. Giygas's lines are based on the victim's lines in the movie. This much is fact, the rest is speculatory.
The final stage of the game is a ******. The Devil's Machine that Giygas resides in is the cervix. If you look at the stage there is an almost too-eerie resemblance. This could be passed off as coincidence on its own though.
Unlock other bosses, there is no graphic for Giygas during the fight. You just see reddish swirls on black in the background scrolling to the side. What you might miss is a very prominent shape that appears in this design: a fetus.
Further, some people claim to hear Giygas's voice saying "Let me out," and "Help me," (people who are apparently unfamiliar with this theory). I can pick them out by they are faint and I have some doubts that it was intentional. Seems like maybe a case of hearing something because you try to hear it.
It follows in the story as well. We are going back to a time when Giygas is weak; we have no chance of defeating him in the present. Doesn't get much weaker than a fetus.
So some people have interpreted all this to suggest that the main characters effectively become abortion robots at the end of the game, killing what may presumably be an unborn person (possibly conceived by rape) who is not, as Pokey says, pure evil (they point out that Pokey lies all the time), but maybe just an unfortunate person that through a hard life inevitably became the equivalent of a thousand Hitlers. Who knows. Further speculation says that when the Devil's Machine is opened, the face that is seen (the main character's) is Giygas's attempt to tell the main character that they could be friends. Perhaps if the baby Giygas had had a friend like the main character, he wouldn't have become the super-evil influence that he supposedly became.
Anyway, interesting theory. I would really like to hear what the creator would say about it.