Discussion: How dangerous are free bags?

So, I was in town today. I bought many clothes, which I put in my shoulderbag. I also went to M&S and bought food, including raspberry jelly, which I also put in my shoulderbag. Long-story short, the jelly exploded and my clothes need some rapid protection - so I needed a plastic bag. The closest place was Clinton Cards, and I hoped the store wouldn't mind some free publicity with me putting clothes I bought at another store in their bag... I went in and asked, and I was told I couldn't have a free bag. Understandable, economically. But the awesomeness comes from their excuse... "We don't give out free bags for security reasons". Security reasons?? Seriously? Yes, apparently.

Which got me intrigued. What security reasons could there be? I was going to make this a top 10, but I could only think of 5...

1) Because it is empty when it leaves the store, it could be blown away by a gust of wind and land on someones head, thus resulting in them running into a wall

2) You could take their free bag, walk outside, and use put it over your head to commit some robbery in another store, thus giving them bad publicity

3) You could take their free bag, put it over your head and commit robbery in their store thus being ironic

4) The free bag could be melted down, and moulded into the last ingredient in some fiendish bomb construction

5) The bag could later be corrupted by being recruited by some evil group for it's own nefarious pruposes

That is all.