I don't think the point of the exercise is to successfully defend the opposing point of view but to make a good-faith attempt to come up with an argument for it without getting your original emotions involved. If you can conjure up a coherent argument for the opposing side (allowing for a slightly different set of priors), that's some evidence that you're looking at consequences rather than being strung along by motivated cognition. If you can't -- and this is pretty common -- that's good evidence that the opposing view has been reduced to a caricature in your mind.

It's a litmus test for color politics, in other words. Not a perfect one, but it doesn't have to be.