No, it's not the father's body. Does that mean he sacrifices a say in his offspring's continued existence? Pro-choice, of course, takes that choice from him.
Hard to take away a choice they never had the right to in the first place.
At what point does a sperm+egg become sapient? To be honest it's probably sometime after their born, the human brain takes awhile to develop, but in the first few months you really are just talking a clump of cells that if you squint really hard is starting to get some of the functionality of a human being. The exact point at which they get that functionality is like the "how much do I have to shave the back of a chair off before it becomes a stool" problem, it's a vague category and a gradient rather than a clear line.
Conraceptives are fine, right? That prevents the potential for a human, so clearly potential-to-be-human isn't the issue.
Morning-after pills are clearly okay, right? That's just recently fertilized egg cells, so clearly fertalisation isn't the issue.
A few weeks? Well then it's basically still just a clump of cells.
20-odd weeks is survivable, usually with extreme medical intervention, but the distinction between patient and corpse is always going to be determined by scientific advances. (Like how cryogenic freezing is killing a person and hoping future medical advances make it not killing them).
Hence the "Hey it's a complex, grey topic without easily defined lines so let's just give the woman the right to safely choose because the alternative is them going for a coat hanger and a bottle of vodka to try and achieve the same end".
And let's not pretend contraceptives are 100% effectively. Unless the argument is that all men should be given SLVs at sexual maturity? And still that's discounting the horrors of rape. An abortion and a rape baby are both potentially traumatic, if a woman decides the former is less so than the latter I'm not going to stop them.
Maybe eventually we'll start growing human babies outside the womb and sex can be made purely recreational and children purely a choice, would get around a fair few problems. Pregnancy is a strain on a womans health at the best of times, is rather unpredictable (miscarriages and all), and disproportionately takes them out of the workforce too, so from both a physical and mental health and economics pov it offers benefits if we can take pregnancy out of the equation. But until then, gotta work with what we got.