I really like Jonathan Haidt's ideas about encouraging people from 2 different sides of an issue but who are both genuinely committed to the truth to battle each other with the intent of letting the truth emerge from the argument. This is extremely beneficial because we are all blinded by our own biases and it is very helpful when the other side helps us to see past them.
This is admittedly difficult to achieve in a forum like hacker news but IMHO it would be amazing if someone could make this happen. The biggest improvements to my own predictive model of the world have always come when arguing with someone who held a contrary view and I'd like to believe that I have returned that favor from time to time as well.