Always consider the audience. When talking to athiests, speak the language of reason.
For many of the listeners, one religion might look as kooky as the other. So it is useless to speak to shades of interpretation of the bible, for instance, because this is not the framework they come from.
As a social institution, is it "just like any other" or are there practices that make it worse?
The more I learn about shunning, the more I am convinced it is an evil practice. We are social beings from an evolutionary point of view. To shun is unnatural and does psychological harm.
Also interesting is how the mind can be conditioned to subsume their natural personality to the group. People often firmly defend the indefensible. How does the mind play this trick on itself, and how can it be overcome? There are the stories on this board of people awakening as if from a fog, and quickly discarding falsehood after falsehood. There is liberation - and loneliness - in this awakening. What is the difference between these brave few, and the many that remain in the comfort zone?
How is a person's behavior affected if they begin to view others as either "redeemed" or "condemned"?
Be prepared to answer the question, in a pluralistic society, if it is right to single out a single group as harmful, just because they are different?