In the revealed Law of God it is pretty silent on this issue in any specific way; as such it is required that we think through these issues thoroughly, with a mind toward justice, i.e. what is right. And that means we have to take seriously a whole bunch of things into consideration: including philosophical matters such as human personhood. Is anything genetically human fully human? If that's the case then then that requires us to consider things such as amputation, the surgical removal of certain things (such as an appendectomy), or even blood transfusion/organ transplantation. At some level we all agree that simple human DNA is not itself sufficient for human personhood. And thus approaching the subject biologically means examining embryonic and fetal development. There are, of course, more metaphysical concerns to be addressed for people who believe in such things, relevant here is the matter of ensoulment; i.e. when (how? and from where?) does the soul come? And there have been many ways to answer that question throughout the history of the Church; the position that the soul is created at conception may be the most common opinion today, but it is far from universal dogma in the Christian Church (and never has been). This is a question that has been wrestled with by Christian philosophers and theologians for centuries.
What I think is dangerous is a kind of ham-fisted dogmatics that is achieved, not by thorough inquiry and consideration; but mere say-so, entirely without the aid of Divine Revelation as we have it through the history of God and His people as recorded in the holy texts of Scripture; and instead by sheer speculation.
-CryptoLutheran