I believe science has decided that the ability to maintain homeostasis is a requirement of life. A fetus has no shot in hell in surviving outside of the womb because it is physically incapable of maintaining homeostasis. As such, it fails to meet the requirements to be considered life. If you're curious, I don't believe brain dead people should be considered alive since they can't respond to stimuli, and they won't ever respond to stimuli.

"Oh, but the fetus has potential to be alive if it just stays in the womb long enough." Fair enough, it's a true that it will eventually become a living thing. But under that logic, ejaculation is a crime because sperm has the potential to become a human as well. A woman's period is a crime because it's the ejection of dead eggs. "Oh, but by themselves they won't become human, so the potential is different." Ignoring that spontaneous conception is entirely plausible, if improbable, a fetus won't become a human by itself either, it needs a host until it reaches viability, which takes at least 23-24 weeks to have a 30% chance at surviving. The vast majority of abortions take place well before this point, and the ones that occur after are usually done because of instances of rape or incest, or because the mother's life is at risk if they carry it through to term.

Furthermore, consider this thought experiment. Let's say you are a space explorer. You come across an alien civilization with vastly superior technology. They're curious about your race, so they give you a proposal: give up your life, and they will make a million humans out of your dna to live in their society. Are you in the right to deny the request? Now let's say you don't need to give up your life, instead you need to go through 9 months of discomfort, ending in bowel-shattering agony. Are you in the right to deny this request? I would argue, in both cases, you should be entitled to decide what happens in your life, regardless of the potential extra lives you may create by doing something against your will. The rights of an actual person outweigh the rights of an infinite number of potential people, solely because potential lives have no consciousness to afford value to them.