The media never misses a chance to make a non-event into a huge crisis. The safes are steel boxes bolted into a closet or cabinet. They either use a card reader where you use a personal credit card and swipe it to open/close the safe (no charge, the reader just needs a magnetic strip with a unique encoding), or they have a keypad where you enter a series of numbers as your personal combination.
The facts are that there is no widespread theft aboard cruise ships. I have never encountered a problem and have never heard of anyone on one of my cruises getting robbed or having their cabin burglarized.
I feel quite safe leaving things in my cabin safe and venturing out. Don't worry about it and enjoy your cruise!