Interesting responses and food for thought. I wonder if the Aircraft Carrier in time will become as vulnerable and irrelevant as the Fixed land based Fortress? Might seem like an odd analogy but since the Romans here in the UK a Fortress was built not only to defend the occupants and control the ground but to be as was said above to be "an overt, visible sign of deterrence and coercion"
The trouble is that although land based forts had a good run every few years someone would invent something to negate them; siege engines, ballistas, undermining, artillery and so on. By WW2 the French had invested a fortune in the Maginot Line and Belgium had its fortifications. Blitzkrieg swept past them glider borne assault troops landed on them and they used shape charges to disable them.
Carrier groups, especially when deployed into the Gulf or close to Korean shores look vulnerable to me. It only takes one lucky hit or an accident of seamanship for a list to negate most of its firepower.