Conair, I certainly wasn't suggesting Knock for diversions, that isn't at all realistic as the infrastructure couldn't cope. This isn't a SNN v NOC thing by any means.
The difference between Shannon and Gander is that Gander is on an isolated island off the coast of mainland Canada, hundreds of miles from major airports and hubs. It is virtually a mid point for many transatlantic flights and has an important role to play. Shannon, on the other hand, sits within the British Isles and is very close in relative terms to mainland Europe also. Diversions etc. into Shannon could easily be dealt with at numerous other airports in this part of the world, they sometimes go to Shannon because it's the first one off the Atlantic, but if it didn't exist they'd just go somewhere else, loads of available options. Ireland isn't the only country in western Europe, believe it or not.
The idea that Shannon plays some kind of pivotal, irreplaceable role in European aviation is no more than a myth. It is occasionally useful, but it is by no means vital and cannot be used as an excuse for running up €100m of debt. It needs to pay it's own way to the same extent the other airports do.