In my opinion the TA has told you lies...................
Have been on the streets of Cancun on my own and felt as safe as here in Manchester. A lot of hotels are on there own complex and too far to walk into Cancun anyway.
If you want real luxury have a look at the Royal Cancun, adults only, no reservations needed for al a carte restaurants, walking distance to Coco Bongos and all the luxury shopping malls, waiter service on the beach and around the pool. Excellent.