Use appropriate source material. This isn't always an easy call. Other sources are perhaps not as obvious. If several members of the list object to the use of any particular source, stop using that source. A rule of thumb for this is, use a source that supports your own position, not one that undermine's your opponent's.
Consideration is the key.
This doesn't mean you have to pretend to agree with anyone, or refuse to take a stand against ideas you disagree with, even vehemently. But keep in mind that those ideas do belong to people who have thought them out over time. Being deliberately hurtful or scornful, aside from being unlikely to win any converts to your position, is rude. Oh, that made you mad. It appears, and suddenly it seems less like a battle of wits and more like a flame war.