There is a sin in abortion. Let's not argue "life or no life." Let's not argue whether abortion should be allowed in cases of rape or incest (less than 1% of all abortions performed). There is still a sin in abortion.
Abortion activists claimed (and based their landmark case on) "a woman's right to her own body." Surprisingly, this defense has not been caught up by attorneys across the country to justify drug use, prostitution, gambling, and all the other so-called "victimless" crimes. Interestingly, the only other group that clings to the "own body" banner is the "gay rights" movement. Unfortunately, perhaps, for both the "pro-choice" and homosexual communities, their basic premise is wrong. "Do you not know that your body is the temple of the Holy Spirit..., and you are not your own? For you are bought with a price: therefore glorify God in your body, and in your spirit, which are God's." (1Co 6:20) If they don't fall under that scripture, not being Christians, then perhaps another one applies—"The fool hath said in his heart, There is no God. Corrupt are they, and have done abominable iniquity." (Ps 53:1)
The real sin in abortion is as basic as sin itself. It encourages a lack of a sense of personal responsibility. Adam started it. "And the man said, The woman whom you gave to be with me, she gave me of the tree, and I did eat." (Ge 3:12) Freud and the psychoanalysts continued the trend, saying its our upbringing or a childhood trauma, or "society's fault." Is it any wonder that many people shift blame for what they do, since even our courts tell women, "you don't have to suffer the consequences of your own sexual activity." If she doesn't have to suffer the consequences, why shouldn't I avoid the consequences of my actions by blaming someone or something else? Hence "the Twinkie® defense," (the sugar made me do it).
When I was working for Navy Recruiting's Inspector General's Office, we interviewed recruits who had omitted things on their application for enlistment. When I would ask why they lied it was extremely rare for one to say, "I did it on my own. I was wrong." Occasionally the response was, "I didn't lie. I just didn't tell the whole truth." Most often I heard, "My recruiter [or parents or spouse or friends] told me to." I can picture them standing by Adam at the judgement, saying "the parents that you gave me told me to sin, so I did it." And I can see God quoting scripture back to them, saying "The son shall not bear the iniquity of the father, neither shall the father bear the iniquity of the son: the righteousness of the righteous shall be upon him, and the wickedness of the wicked shall be upon him." (Ezek 18:20) God's law is that sin has consequences. The blood of the Christ may cover the sin, but some of the physical consequences may still be required of one (like having a baby).
Abortion is a sin because it tries to violate God's law of consequence. Interestingly, that law is proven by the abortion and irresponsibility rampant in this country today. God says, whether it be truth, sex, or psychobabble, "whatever a man sows, that shall he also reap." (Gal 6:7)