Why Don't They Just...?

As part of a new, intermittently-recurring series, I bring you...

Why Don't They Just....?

Because "common sense" is an oxymoron!

Yet again this week, airline passengers had to restrain a nut job using seatbelts and plastic handcuffs, and even then had difficulty keeping him in check. So, what I want to know is...

Why don't airliners just carry a roll of duct tape as a matter of course?