Don't be a fascist. Try and keep an open mind, and when you disagree, simply be polite about it.
Just don't open your mind so far that your brain falls out.
If your debate opponents aren't even willing to concede the existence of physical evidence or the relevance of basic logic, then you are not going to achieve anything useful by pretending like their arguments have any sort of useful information in them (unless you're studying the psychology of the willfully ignorant).
And politeness works best when it is being practiced in both directions (referring to common reactions by people who think their faith is being attacked, not your post).
I, for one, have spent many years trying to be polite to certain aggressive creationist relatives. I have not seen any evidence that my politeness has caused them to consider my views with any more validity. On the contrary, they tend to regard my politeness as evidence that I do not have confidence in my arguments, and that encourages them to attack.
On the other hand, if I go out of my way to make them look like idiots in the eyes of their peers whenever they open their ignorant mouths, I can at least get them to keep quiet when they are within my earshot - which has done wonders for my stress levels & for the general level of discussion at family gatherings.