Imagine the scene at an airport.
"Hi, I'd like to check in my luggage."
"Sorry, is that a suitcase? I'm afraid I can't accept any suitcases"
"It might have a bomb in it"
"But it doesn't have a bomb in it. I packed it myself"
"I can't take that risk. There have been too many cases of suitcases with bombs in for me to take that risk."
"Can you scan it and check that there isn't a bomb in it?"
"No, I don't have time for that"
"Well, what do you suggest?"
"You could take each item out of the suitcase and take them separately"
"What? That's ridiculous, I must have fifty things in the suitcase!"
"Or, you could airmail the suitcase to the destination. In fact, the airmail goes on the same flight that you are on, so it will get there at the same time"
"So if there was a bomb in the suitcase, it could still blow up the plane..."
"I suppose so, but that's not my problem. Tell you what, why don't you just wrap the suitcase in cellophane."
"Wrap the suitcase in cellophane. I've heard of lots of cases of bombs in suitcases, but I've never heard of a bomb in a suitcase that's wrapped in cellophane."
"Surely that's no protection if there was a bomb?"
"Oh, absolutely not, I expect. Shall I get you the cellophane?"
"This isn't security at all. This is just a pretence at security which just ends up wasting everyone's time and causing me irritation and frustration."
"Always happy to help."
What is this really about? Let me give you a clue: I recently tried to send a zip file to someone whose mail server refuses to accept zip attachments.