I often use the snippet below when addressing pro-life reasoning online or in person. One can obviously go in-depth on any number of pro-life topics and responses to pro-abortion arguments, but I like to have something short yet comprehensive handy. Feel free to use without attribution if you would find it helpful in any way. Hat tip to Stand to Reason for the 2nd and 3rd paragraphs.
Pro-life reasoning is simple and accurate: It is a scientific fact (http://tinyurl.com/yfje8lq ) and basic common sense (what else would two human beings produce?) that a new human being is reproduced at fertilization. Seriously, go check out any mainstream embryology textbook. I’m too pro-science to be pro-choice. Based on the settled science, it is then simple moral reasoning that it is wrong to take the life of an innocent human being without proper justification, and that is what happens during 99% of abortions.
The situations surrounding abortions are psychologically complex (pressures on the mother to abort, economic concerns, etc.) but morally simple (you don’t kill unwanted humans outside the womb for those reasons, so you shouldn’t kill them inside the womb for those reasons). Their size, level of development, location and degree of dependency are not reasons to ignore their right to life. Arguments about “bodily autonomy” ignore the body destroyed in the abortion.
In other words, it is wrong to take the life of an innocent human being without proper justification. Abortion does that. Therefore, abortion is wrong.