There is really no point in this unless you are arguing with someone who is trying to be honest to begin with. In that situation you don't need so much artifice anyway.
Well, I'd say there's a continuum of honesty. And intellectual generosity tends to beget intellectual generosity in the other person--and, for thoughtful undecided onlookers, makes them more amendable toward considering your side.
For instance, speaking from both sides of the experience, someone who is engaged but being sniping or nasty in a political debate might well see that you're giving their point an honest go of it and in response clean up their act.
And even if they're lost beyond all hope, there's only a limited amount of fun to be had in poking holes in the small without really addressing their motivating concern.
