My debate opponent stated that the nervous system isn't developed until 20 weeks

That's complete bullshit. An unborn baby starts moving its limbs independently by 9 weeks. By 11 weeks it's able to open its mouth and suck its thumb. How does that happen without a nervous system.

That "the fetus feels no pain" is the same crap that vivisectionists preached in the last century when they were trying to justify their cruel experiments on animals. "That dog over there howling and whining and trying to escape the pain? Yeah, that's just an automatic response."