More than the sugar or calories, it's the high fructose corn syrup that's the danger. There are these natural sodas out there like the "Izze" brand which are just carbonated fruit juice and taste just as good.
People probably gravitate to soda because tap water is so foul. I had that problem when I was growing up. I wouldn't drink tap water because I thought it disgusting. And I was right. We purify our water with reverse osmosis and I love it now.