As a general matter I don't challenge people of faith if I differ with them on the "why" question. They have their faith, its theirs to explore. Now, if I am challenged by some one else I'll play but I don't initiate that with another (though I'll step in sometimes as a third party when some one else gets challenged... the point is, I don't volunteer until some one asks, demands, provokes etc)
The non-believer isn't exploring anything, they've declined to do so or explored a bit and then shut the book on the topic.
W/myself.... constantly. For my part, exploring a bit, deciding I believe and then shutting the book is no different that the non-believer who did the same.