The new ones are shiny. Sailors like shiny things, it makes them feel important. In the eyes of the rest of us, they're a colossal waste of good money; the old ones are obsolete, but they'll do for the job we ask them to for a good while yet unless there's another shooting war at sea.
I'm not sure about that, a good number of people support them. I think their primary purpose, enabling power projection, is a worthy cause. Old ships need replacing otherwise costs spiral I believe.
One carrier could provide more firepower than Britain’s combined fleet of current aircraft carriers and will be more potent than the majority of the world’s national air forces, meaning that these vessels will be the most powerful warships ever built by a European country.
A good quote on the matter is;
"Britain’s ability to project naval power in distant waters has been crucial to its foreign and defence strategy for centuries. At first, this was accomplished by wooden Men-O-War, which were followed by ironclads, then Dreadnoughts, and today, by the aircraft carrier and its escorting naval squadron. Since the end of the Second World War, the deployment of aircraft carriers to the Falklands in 1982, to Bosnia and Kosovo in 1995 and 1999, Sierra Leone in 2000, and to Afghanistan in 2001 and the Persian Gulf in both 1991 and 2003, has confirmed again and again that British overseas involvement would be impossible or greatly reduced without this unique capability. The aircraft carrier is and will remain the armed forces’ backbone. Currently, the Royal Navy holds two such vessels, but these remain smaller in comparison with the supercarriers operated by the United States. In reality, they are relics – although since upgraded – of the Cold War era. But this situation is not to last much longer, for the Ministry of Defence has underway a naval programme to replace these three smaller vessels with two new supercarriers of its own. Britain’s current ‘Invincible’ class aircraft carriers weigh approximately twenty-two thousand tonnes and carry an air-wing of twenty-two aircraft, including both ‘jump-jet’ ‘Harrier’ strike-fighters and an assortment of helicopters for reconnaissance and air-to-surface attack. The new aircraft carriers will be three times bigger, weighing approximately sixty-five thousand tonnes, and equipped with over fifty aircraft, forty of which will be the new Anglo-American ‘Lightning’ strike-fighters.
The ability to deter or coerce is also critical, and the Royal Navy’s fleets will continue to have an unmistakably physical and threatening presence when deployed overseas. When located outside a problematic country’s territory, the very existence of an aircraft carrier or nuclear submarine, capable of firing cruise missiles, may be able to cajole autocratic regimes into abiding by the will of the international community, and/or that of Britain. Such a naval presence provides London – or, the European Union – with a modernised version of the ‘gunboat diplomacy’ of lore, a tactic which had its origins in the Victorian era, where such displays typically involved demonstrations of naval might to symbolise political will and determination. The mere sight of such power almost always had a considerable impact, and it was rarely necessary for such boats to use other measures, such as demonstrations of cannon fire.
Yet the most important and profound consequence of Britain’s upgraded, twenty-first century fleet, is that foreign interventions will become more achievable. When necessary, Britain will be better equipped and able to act unilaterally, as it did in the Falklands War, or in the Sierra Leone intervention, when rebels were set on slaughtering the people of Freetown. But also, a powerful navy will provide Britain with unprecedented influence in the evolving strategic culture of the European Union. Britain and France already cooperate on a whole range of military issues, and France will work with Britain to build its next aircraft carrier, by using British designs."
Frankly, I think the need to replace the Invincibles with something much more capable is quite pressing. If we want to retain a top spot at the table of world military powers, we need such assets, especially when many countries around the world are building their own large carriers.