Abortion is unlike any other issue debated today. Millions of American women have aborted a child, and the pain, loss, and emotional need to justify what was done, both on the part of the mother and on the part of her loved ones, is strong and deep. This means that, in any debate, you may face an invisible thumb on the scale so that even the best logic will fail to persuade.
The best you can do is arm yourself with the facts and deliver them in what you hope will be a winning way for your audience -- meaning you will need to make your case, in most instances, not in the language of faith or religion but in the language of the post-modern secularist.
What follows, therefore, are the best arguments from science, the law, and women's rights to advance the pro-life case against abortion.