To me, the difference between what I read blumkvist to mean by debate and what I read you to mean is that blumkvist's debate is more like your discussion - teasing out the details, attacking the issue from a different angle to find out what the limits are, finding not just the flaws and shortcoming, but also the benefits of whatever is being discussed.

Often this is done by playing devils advocate or by playing dumb and getting the other people to really explain their viewpoint. I do this too when I either don't properly understand what is being presented and I want to encourage others to flesh it out and explain it in a way that I get it, or if I see the ideas as being too vague or risky and I want to make sure all of the pros and cons have been properly considered. Often I will then concede, because the idea really was a good one, but sometimes I dig in if I feel like it isn't being resolved.

I'd say I go looking for a discussion in these cases, but its not up to me to judge - only other people can tell you if I do it tactfully or not. I'll make an effort not to be too confrontational.