Why are fizzy drinks BAD for kiddies?

Granny-B, my voice of reason mother, informed me this weekend that fizzy drinks, be they sugar free or not, are a HUGE NO NO for Gioia!  Somehow instinctively I agree, but I want to know why exactly?  My mom watched a show on TBN where a Dr said that it stunts brain cell development! I have been looking for information online but have not found anything concrete yet. What are your views mom's? Either way Coke and TAB has now officially been banned from my shopping list, I can't drink it in front of her and then say no when she holds out her fairy cup.  100% fruit juice and water will be encouraged from here on out.  Hold thumbs, this could be rather hard, for me, not Gioia.

UPDATE:
Link from Carike - Thank you to my super duper mommy friend...this certainly helps me understand! Click on this link if you want to know why it is reckless for us as mommy's to give your children fizzy drinks.  http://blogs.mirror.co.uk/dear-miriam/2009/06/why-parents-shouldnt-give-chil.html