For me it feels better to agree with someone rather than disagree, so I have to be careful not to sugarcoat things too much. On the other hand, if I loved to debate with people, I'd probably want to be more careful about being too blunt. The other problem with religious debate is that it can quickly get personal. When you present something opposed to someone's core beliefs it may feel like an attack even if it isn't. What starts as a debate can quickly turn into a flame war.
People take on whole different personas online than they are in real life.
It's easier to convey your ideas bodly online because no one knows who you are, and you don't know them. In a way, expressing your ideas bodly gives them license to do the same. So be prepared for equally bold statements coming back on the other side of the issue. AND you want to be friendly with them. Once they have that impression of you stuck in their head, its a whole lot more difficult to have a meaningful conversation.