The perception that these characters shouldn't be touched by anyone other than Alan is both absolutely understandable and deeply flawed. As good as these characters are and they are very good indeed, one could make the argument, based on durability and recognition, that Superman is the greatest comics character ever created. But I don't hear Alan or anyone else suggesting that no one other than Shuster and Siegel should have been allowed to write Superman. Certainly Alan himself did this when he was brought on to write Swamp Thing, a seminal comics character created by Len Wein.
Leaving aside the fact that the Watchmen characters were variations on pre-existing characters created for the Charleton Comics universe, it should be pointed out that Alan has spent most of the last decade writing very good stories about characters created by other writers, including Alice (from Alice in Wonderland), Dorothy (from Wizard of Oz), Wendy (from Peter Pan), as well as Captain Nemo, the Invisible Man, Jeyll and Hyde, and Professor Moriarty (used in the successful League of Extraordinary Gentlemen). I think one loses a little of the moral high ground to say, "I can write characters created by Jules Verne, H.G. Wells, Robert Louis Stevenson, Arthur Conan Doyle and Frank Baum, but it's wrong for anyone else to write my characters."
The whole point of having great characters is the opportunity to explore them more deeply with time, re-interpreting them for each new age. That DC allowed these characters to sit on a shelf for over two decades as a show of respect is salutary, but there comes a time when good characters have to re-enter the world to teach us something about ourselves in the present.
- J. Michael Straczynski