Ok then, could you tell me why airline pilots have a licence ? From my personal experience, i'd say because you have successfully completed a long training, you fulfilled all the CAA regulations and passed your class 1 medical. Why is all this important, because you play a crucial role in that plane, as you are responsible for the lives of pax and crew behind you... now, if there is a problem, or if you screw up, the cabin crwe are there to try and make things as painless as possible. Within our industry the safety of the passengers and crew is of primordial importance and all crew members must be able to reassure passengers, provide for their comfort and safety, in particular if there is an incident which might upset or frighten them.
Now if you believe that cabin crew are only their for customer service of for your tea and coffee, then I wouldn't like to be part of your team on a flight... Cabin crew have an extremely important role in an aircraft and not everyone can do the job, which is why a licence is a good idea. I might just point out that CRM and team work is also part of the ATPL course...