Paul Graham has written a short yet striking article, How to Disagree, which could help us all improve the tone and content of debates we pursue online. He classifies comments expressing disagreement into a Disagreement Hierarchy with seven levels, from insults and ad hominem attacks at the bottom through to counterarguments and reasoned refutation of your opponent’s central point at the top.
As he points out, being aware of this hierarchy will help not only to recognise weak arguments made by others, but to make your own case more powerfully and more politely:
[T]he greatest benefit of disagreeing well is not just that it will make conversations better, but that it will make the people who have them happier.