I think you'd be surprised about how many people would keep bringing it in anyway after being clearly and repeatedly told it will be thrown away (substitute any other clear instruction here where people will still insist on doing the opposite and be shocked when it's not allowed but continue to try the next time and the next). That's logical people brain speaking - it's a poor model for the behavior of probably at least 10% of the population. I've seen it in person more than enough.