I do get it that you need to find a way to be diplomatic so that you don't put them on the defensive about their own drinking. Unless you want to.
I would avoid declarative statements against drinking, even if it's what you think: "Drinking is bad for for you," "People who drink alcohol will all go to hell!", "Drinking is stupid!". Stuff like that. Don't be an activist about your new non-drinking status unless you are prepared to argue. You realize, of course, that you can't argue with someone else's beast!
Just be matter of fact. You are what you are. You might say, "I just don't enjoy it any more", or "I just don't want to drink." Or, better still, "I have more fun since I stopped drinking." Or, whatever you feel comfortable saying.
Most of us who haven't been drinkers in a long time no longer feel the need to explain ourselves. I've met up with people I used to drink with, and no one has ever challenged me about being a non-drinker. I'm just one of the people at the table who doesn't order a drink.
FT