Because before the image/event many truly do not think of it as a baby. That is when you are raised hearing that its ok for the 1st trimester, so so for the second and bad for the third, as I was, you believe what you are told in the home.
Its very nebulous and you don’t think of it truly as a baby, the “mass-o-cells” logic holds sway. And there is reason and debate.
Then, if you are like me, one day on a business trip to CA you see a protestor holding a gruesome sign showing precisely what it is we are talking about.
In that moment all the BS you were told growing up vanishes, and is unable to return.
But, a simple lesson in biology could also do the same. A sperm meets an egg. Immediately there is cell division and a multitude of chemical reactions that proceed for nine months in the case of humans and the end result is a baby.
Interrupt that process at any point and there is no baby.
Furthermore, most individuals, from their earliest days, have an innate sense of right and wrong. This has been psychologically proven through experiments time and again.