They actually do discuss that on the pro-life side. They point out in that case, where's the line? Calling it "viability" is fuzzy because, are old people / disabled viable; and also because preemie babies are increasingly likely to survive earlier and earlier.

For example, just a few weeks ago, the world's most premature baby (with 0% chance of survival at the time, completely unviable) just had his 1st birthday.

https://www.washingtonpost.com/lifestyle/2021/06/23/prematur...

I understand that's about the earliest viability will ever be, because if there aren't working lungs, it simply can't survive.

On the other hand, perhaps technology will advance to the point where even a fertilized egg could grow outside the womb. Then abortion might turn into "take this thing out of me and find somebody else that wants it."