Here's an argument: People should not be impeded by non-people.

The fundamental philosophical argument in favor of abortion is that reproductive cells are not people. The argument is over the extent to which this is true and the duration over which it is true. The fact that it is true to some extent is taken as given by almost everyone.

Very few in the modern world call male masturbation an act of genocide, in spite of the death of millions of sperm cells.

Some people argue that at conception, there is a dramatic change and the clump of cells deserves moral rights beyond those of reproductive cells. At the other extreme are those who argue that the moral status of the unborn changes at birth and no earlier, since prior to birth the fetus lives a parasitic existence within the mother's body and is aware of nothing beyond the womb.

More moderate folks declare that an unborn child cannot be a person before it is conscious, and debate at what week consciousness is most likely to develop, intending to bar abortion after that point.

I am in that third camp. I don't feel that a 'soul' (and therefore personhood) can predate consciousness and I don't believe a soul is set out for every child at conception. On a metaphysical level, I don't feel that there's anything for the soul to 'attach' to prior to consciousness - any soul that was set out at conception would be disappointed, but not harmed, if that child were aborted. On the other hand, I think consciousness probably predates birth, making the debate relevant. It would be a very disappointing existence if one were only around for a few days or weeks before dying.