Depends on the group. When I hear the "sacred" comment, it's often from Catholics who (officially) oppose capital punishment. With other groups, they talk more about "not killing innocents" and thus leave room for killing as a punishment and after legal review. They are two different cases, however finely split are the hairs.

The counter to your argument might be: if life is NOT sacred, then why punish murder or manslaughter?

Seems to me the real issue is still when that fetus acquires its own legal personhood. From a scientific point of view, it seems to me that this would either be at birth or at "fetal viability," whatever that may be. A reasonable debate can be had around that issue, but I never hear it discussed in those terms.