Finally I scared myself enough that sugar drinks cause pancreatic cancer (no evidence but I'm still scared) and high fructose corn syrup causes fatty liver disease, which I actually do have, which in turn can lead to cirrhosis and/or liver cancer.
From that I basically scared myself straight. I started drinking a lot of unsweetened tea actually, and then substituted a little sweet tea for Coke. Eventually I've just broken the habit of drinking Coke every day and drinking tea instead and these days a lot of water as well.