I suppose it's an underlying principle of good faith discourse. And good faith discourse is an absolute requirement to have a meaningful conversation or debate that moves (whatever) things forward.

Part of the reason that political discourse is currently so polarised and pushes us towards bad outcomes in our societies (thinking particularly of US and UK here, but I'm sure it applies elsewhere), like the recent riots in the UK, is that so much of it is bad faith, dishonest, assumes the worst of others, casually alienates to score points, etc.