John McCain has taken two irreconcilable positions.
Either the right to life is a matter of human choice or it isn't. If it is, as McCain's position suggests, then its sole claim to protection is positive law -- not natural law.
If this is true, then there is no objective standard by which the degree of misfortune can be consistently judged -- giving credence to the notion that the right to life ought to be subject to the choice of the mother, and not the government, and certainly not God.
It may be impossible for your mind to reconcile the fact that individual life begins at conception and the self-defense rights of a woman or girl who has been raped, and such either or mentality does fashion the irreconcilable, but courts and natural law deal with this sort of thing often, in reality.
Our technology has not reached the point of being able to successfully transplant an implanted embryo, yet. We will reach that point if civilization continues for another twenty years. At that point the way society deals with what you deem irreconcilable will change from the reality of today, if we adopt perspectives now which value the little ones from conception onward. But that doesn't relieve the reality of today's conflicting rights of the woman/mother and the rights of the newly conceived.
Presently, the debates over embryonic stem cell exploitation, which Mitt Romney has just as convoluted in his supposedly 'now' pro-life mind, are heading in the wrong direction under democrat, liberal demands. Even men like Orrin Hatch are using an unclear definition to exploit the situation and authorize the dissection of alive human embryonic aged humans who have not been implanted in a human body. [And to illustrate how complex the issues can get, I referenced 'human body' instead of female body because the sexual degenerate class are already trying to get embryos implanted in homosexual male surrogates. And some research technology has tumbled off in that direction!]
If our culture does not now take the perspective that even embryos conceived in petri dishes are humans at an earliest age, then the resolution of conflicting interests, the rights of the newly conceived and the self-defense rights of the impregnated will not be correctly resolved because one class is becoming more disenfranchised rather than more enfranchised. Fighting embryonic exploitation now works to enfranchise the newly conceived and thus move our technology/research int he direction of learning how to protect even an implanted embryo while recognizing the right of a raped female who becomes pregnant from the crime of another to defend her life by not being forced to continue a pregnancy which increases her mortality risk through no fault of her own.
You may not wish to consider the above reasoning, for whatever reason you hold privately, but that is a more in-depth look at the complexity and the conflicting compelling interests. The idea way to deal with pregnancy from rape or incest is to save both innocent parties, but our technology has yet to relieve courts of that enigmatic case, so the courts settle such problems by assigning greater or lesser interest/right based upon the societal values, and our current direction in values is into the democrat/liberal gutter. You won't change the trend by demanding and either or of extremes, but many continue to harbor that dream.