[Here is a hypothetical example for you - I see a great QR Code on a poster for Company XYZ - I am a teenager with nothing better to do so I go home, create a QR Code that links to a competitor of the original code or an adult website or a militant group - and in the middle the night i quietly take my glue and neatly paste my code over top of the existing code.]
Will they paste such codes in all of the magazines as well? Or on other concrete products such as televisions, beer kegs, licenses, business cards, credit cards, etc?
As an adult, I know that if I do click on a code that leads me to an inappropriate site, I'll have the common sense to look at the code more closely, and notice that somebody decided to paste a fake code over the actual code. And I won't make the same mistake twice. I imagine most kids will catch on quickly as well.
Your logic is very flawed, DM. Try again!