What do we actually know?

Edward de Bono is a famous philosopher and thinker. He coined the phrase "lateral thinking" and teaches the importance of 'thinking about thinking'. I heard some feedback from one of his courses which taught a logical way of separating up a discussion into types of discussions so that the meeting could be fruitful rather than the usual messy argumentative style. He called these topics after coloured hats, one for creative thinking, one for negative aspects, one for positive, one for gut feel, one for information and one for the actual struture of the other coloured hats.
When we were talking about it, the person who was telling me this said that we should try a 'white hat' exercise which means we should list what we actually know about something, in this case Speed Cameras. Somebody said, "we know that they are there to raise money", at which point my friend questioned whether we actually knew that or whether we just thought that. After a similar process for other statements, we realised we only actually knew one thing about speed cameras and that is that they detect people travelling above a certain speed. I found this interesting because a lot of our discussions, arguments or techings are filled with statements that we either think are true or otherwise we are unsure but state them as fact anyway. This makes the discussion almost pointless. You can end up with two people arguing from two equally untrue positions rather than separating fact from opinion or belief.
A lot of what we say we know comes from what other people have told us and we have various reasons for believing it or otherwise but when we are talking about important issues, we shouldn't assume a trustworthy source is definitively correct and talk from that perspective.
I sometimes wonder whether discussions about evolution or Biblical interpretation etc would be much more beneficial if we only thought about what we actually know!