I've found myself in a pretty heated abortion debate. I've had no problems finding inconsistencies in most of the arguments, but I'm seeing no progress made, and it's taking quite a bit of time to answer the arguments, especially with things I've already said a number of times. I'm not seeing an end on the horizon. My first question is how do you explain to a non-Christian that life begins at conception? The other is when is the right time to end a debate and how is the best way to do it?
I typically answer the question of when life begins by using the Scriptures. See: How to Misunderstand the Bible under "Abortion" for a sample list. A child in his mother's womb is still called a child in the Bible. The child is not an extension of the mother since the child and the mother have separate DNA. So it really comes down to how much growth by an individual is necessary before the label "alive" is placed on him. It is pretty easy to show that any selected point after conception is really an arbitrary choice. It certainly isn't a choice proven by the Scriptures.
When dealing with non-Christians, the question is that if an embryo is not alive, then why is it taking in nutrition and growing? Since we grow right to adulthood -- and then grow outward for many of us -- at what point is that person not a human? Again, since all the DNA is present at conception, the points are arbitrarily selected by those supporting abortion.
One of the problems we have with debates is that we don't want to stop until we have "won," which is usually defined as persuading the other person to our viewpoint. It rarely happens because as a person loses ground, there is a tendency to dig in, regardless of whether the position is defensible or not. Rather, we need to let go of our pride and see things as God taught us: "I planted, Apollos watered, but God gave the increase" (I Corinthians 3:6). My job is that of a farmer. I look at the field as it is, and move it a step closer to harvest. For some people, I'm doing good if I have a chance to prepare the soil. For many, it is an opportunity to introduce a thought that comes from the Bible. Of course, the greatest joy is to be there at the harvest, but even in harvest, the glory is God's and not the harvester.
I make a point, if it is considered, I continue. If it is flatly rejected, I move on. When a discussion spins back to repeat itself, I move on. I look at it this way: there are white fields to be harvested and I have limited time, so why spend valuable time on one stubborn plant? This is what Jesus told his disciples to do. "But whatever city you enter, and they do not receive you, go out into its streets and say, 'The very dust of your city which clings to us we wipe off against you. Nevertheless know this, that the kingdom of God has come near you'" (Luke 10:10-11). Jesus and his disciples did not stay where they weren't making progress. There were too many places that needed teaching and not enough time.
What I want to be able to say, is that I did my best at that moment in time. Then move on and pray that God sends someone after me how can make use of the little I've done.
I can't think of a set way to end. Much depends on the nature of the discussions. Some I just let die. Some I'll point out the missing logic in a position and then step away. The ones to really watch out for are the steamrollers. Those are the people who when you rebut their point don't address your rebuttal but instead bring up five new points. These I'll answer one or two of their points and list the point they still haven't addressed. If the reply is still more new points, then I'll just point out that this has turned into a monologue and not a dialogue and then leave.
When a person turns to personal attacks, I ignore them. If that is really all his argument is, I walk away. "Reject a divisive man after the first and second admonition, knowing that such a person is warped and sinning, being self-condemned" (Titus 3:10-11). Notice again that you don't lock horns and stay.
By walking away, I mean that I don't feel that I need to have the last word in a matter. I figure that others can see what I can see. They can figure out that the replies after mine didn't answer my points, so there is no need for pointing it out. More often than not, when a person doesn't have a good reply, they end up making themselves look foolish with railings.