"Sometimes we just want to chew things over, throw stuff out, play with ideas. lConversation isn't a randomised control trial."

I think you're talking about speculating or hypothesising here, Cringe. But speculation often leads to opinion and far too often opinion can lead to the logically false position, "I want it to be true ... therefore it is true!" I strongly suspect that most political ideology is based on such a logical fallacy ... but that's just speculation!