Liberty and personal responsibility are precisely the factors the OP was referring to.  How much sugar and how many calories one eats/drinks is a PERSONAL CHOICE.

Are you seriously trying to suggest that people aren't cognizant that consuming more calories in a day doesn't equate to more weight gain??  And that lots of sugar might contribute to other health problems??  

And even if you ARE trying to suggest that, then the government's role would be to ADVISE people about those facts.  Not use the heavy hand of government to unfairly tax a product that's PERFECTLY FINE in moderation.  

People can die from ingesting too much water too.  Do you favor punitive and selective taxation on it too?