If one is against all abortions no matter what.
In my experience, the people who are against all forms of abortion are typically religious nuts and ideologues. These are the people that claim that a second after conception, some magical spirit enters the fertilized egg.
Most rational people understand that there is a difference between living tissue and an individual. And most rational people understand that the line between going from living tissue to an individual is not perfect. Is it 15 weeks? 20? 25? it can be debated, but it certainly isn't 1 second after conception and it's not 1 second before birth.