The argument that abortion should be illegal goes:

A fetus is a person.

Killing a person is bad.

Therefore, killing a fetus is bad.

I believe that consciousness is not an all-or-nothing thing. A newborn baby is most likely a significant fraction of a person. Certainly enough to be important. A fetus early in development is not-a-person enough to ignore. Also, I don't believe that killing a person is bad, at least not intrinsically. It's bad because someone who is dead can't be happy, but preventing abortion is not the best way to increase the population. Getting pregnant and getting an abortion is morally about the same as never getting pregnant in the first place.

Of course, just because death is morally neutral doesn't mean birth is. Is there any way to tell how unborn babies feel? If the last trimester is basically keeping the baby in solitary confinement for three months, then you shouldn't stay pregnant that long unless you plan on letting the fetus be born and have a life worth living.

I argue that all human lives have moral value

Taboo human. Do you mean self-aware entity? Entity capable of feeling emotion? Entity containing a large number of copies of a double helix structure that contains a very long and specific series of nucleotides?