You're killing a (potential) person, and that's never something you should contemplate unless there is a very, very good reason.
'Potential' people huh? Interesting. But how, exactly, do you define a 'potential' human being? Is an egg a potential human being? What about a sperm? How about an egg surrounded by a bunch of sperm that are in the process of trying to penetrate it? Or is it the precise instant that a sperm could be said to have penetrated an egg? Ultimately, everyone has to draw the line somewhere.