Thanks for your reply, Mike, appreciate your thoughts.
At the risk of sliding helplessly into off-topicdom, I must say that 'damn' is not short for 'damn you'. Damn means to condemn, it exists quite happily on its own. If you have "lies and more damn lies" you are not saying "lies and more damn you lies", you are saying the lies are damned, or condemned.
Its religious use is not profane, though it has been appropriated as such since. Its past tense is 'damned' (eg. condemned to hell, or to peeling potatoes):
"And he that doubteth is damned if he eat, because he eateth not of faith"
Then there is the act of 'damnation' itself.
"and they that resist shall receive to themselves damnation"
Things or people can be 'damnable'. 'Damn you' is just a phrase that uses the adjective - 'damn'. I concede that you are probably correct that the word 'damn' is not uttered by vicars all over, but only because its augmentative versions are more useable in a religious context: damnation, damned etc. - perfectly acceptable uses in front of the congregation, I'm sure (hmmm - edited to add this link
Lew - thanks also for your useful answer. My problem lies in two characters saying the same thing, so it has to be a fairly common word. There may indeed be a problem (but as you say, probably only with the more prudish), though the more I look into it, the less bad a word it proves to be. However - it is perception that matters.
'City of the Damned' ran in 2000AD in the early 80s - when kids still read it (admittedly older than the younger end of the DFC readership). I am not worried about the 11 and 12 year olds - which is who my strip is aimed at, but their younger brothers and sisters - who will also read it - I admit that does worry me a little. I am definitely giving it a lot of thought, and am leaning towards changing it rather than upsetting a minority.
While I think the word 'damn' is actually fine for 10, 11 and 12 year olds, I admit, I do not like the idea of a 7-year old going around using it as a new word they've learned from my strip.