I do agree that QR codes can be used for trolling, but there's absolutely no reason you can't inspect the URL before visiting a link from a QR code - all that's stored in the QR code, after all, is the URL!
The trivial technical solution is a QR code reader which tells you where you're going before it sends you there, which ZXing (the Barcode Reader for Android) and several iOS QR readers already do.