I think what you say there about justification is really interesting. I ALWAYS feel the need to justify or explain my actions or whatever and haven’t ever really thought about why.
I keep it simple “No thanks, I don’t drink. I’ll have a sparkling water” or something to that effect. If they ask why or are pushy I just say “I feel better when I don’t drink” or even “my body doesn’t react well to alcohol”. Both are true and don’t get into my business too deeply.
I have actually said “…because I don’t want to die young like my mother did” and it shuts people up pretty fast.
But usually I just say that I think it’s better for me. Usually I get a response like “that’s great, I wish I could go that” and I want to shake them and say “if you really mean that you CAN do it”
“I’ve had enough drinks for a lifetime”. I find people not only show respect but also admiration. I’ve lost count of the number of times people have said “I suppose I should drink less really”.
I saw a friend in a supermarket who knew I was sober. He had a trolley full of booze and said “I wish I could give it up, it costs me a bloody fortune!”