Is it worth arguing with theologians?

Over at Daylight Atheism there's a discussion about original sin. This is one of those fascinatingly odd ideas of Christianity that defies logic, though it's endlessly debated by earnestly learned theologians. I piped up in the comments to the effect that I didn't see the point of the discussion, and was roundly rebutted. Such debates can be interesting in a "let's see how far we can get with this puzzle" kind of way, but I don't see how they could sway those taking part. People who are prepared to argue at length about these issues are probably already fairly entrenched in their views.

Maybe the idea is to say something like "OK, let's for the sake of argument assume that God exists, and explore the ramifications of that assumption." But in what way is pointing out the logical inconsistencies of those ramifications likely to lead theists to question the initial assumption?

Let's assume for the sake of argument that there are fairies at the bottom of my garden. What is the point of discussing what they eat in the winter or how long it takes to dry off the dew from their wings in the morning before they are able to fly? Can you really have a useful discussion with someone who believes they have rational answers to such questions?

My fear is that by conceding the initial assumption, albeit temporarily, we also concede the legitimacy of the subsequent arguments, when such legitimacy is clearly unwarranted.

I'm an equal-opportunity sceptic. My stance is that we should deal even-handedly with creationists, alt-med proponents, psychics ... and theologians. It was pointed out to me, however, that though the participants of such discussions are unlikely to be persuaded from their respective positions, it is likely that there are others observing the discussion, and therefore it's useful to pursue the arguments for the simple reason that many agnostics - and even firm believers - have come to doubt their previously unchallenged beliefs by hearing them questioned.

This fits with my established opinion that religious fundamentalists (creationists, for example) should be publicly challenged because it alerts the religious moderates that nonsense is being promulgated in their name. So in response to the question posed in the title of this post, I hereby revise my answer to "yes".