I maintain that debating fetal personhood is a huge mistake because it goes down a philosophical road where you can’t clearly define things like when someone feels pain.
There is a much simpler reason to make abortion legal- for the same reason it is not legal to harvest a corpse’s organs without the person’s consent before they die or the reason you can’t be forced to donate a kidney. Being forced to use your organs for someone else’s benefit against your will is illegal in every other situation. Even if it means a human will die without them. That doesn’t matter if it is something that will eventually develop into someone with full human rights or if it has them already. It’s just not relevant. It’s about the rights of the person whose body will be used.