Avoid debating or arguing with a blindly naive person

Especially when they are the ones that initiate the discussion.

There are only two possible outcomes in this situation.

1. You come out of it feeling a tad bit idiotic for getting involved in the first place
2. If this was a done in public you will ONLY come out of it looking like a bully

But hey, sometimes its an unavoidable situation which you must deal with the consequences after, that is the ultimate test.