Christians believe that a god exists and was interventionist enough to start a religion that taught the truth about him, so why wouldn't they expect him to at least also be interventionist enough to prevent that same religion from disappearing? And I'm not sure how, given someone already believes in an omnipotent interventionist god who's revealed his will to mankind, also believing that he'll perform a particular intervention in the future is "ridiculous" - do you have a theological argument or one based on the bible for why only an idiot would think God plans to make the rapture happen?