I guess you're right, the body doesn't create carbonic acid... except when it does. And it does.
Carbonic acid is an intermediate step in the transport of CO2 out of the body via respiratory gas exchange. The hydration reaction of CO2 is generally very slow in the absence of a catalyst, but red blood cells contain carbonic anhydrase, which both increases the reaction rate and dissociates a hydrogen ion (H+) from the resulting carbonic acid, leaving bicarbonate (HCO3) dissolved in the blood plasma. This catalysed reaction is reversed in the lungs, where it converts the bicarbonate back into CO2 and allows it to be expelled. This equilibration plays an important role as a buffer in mammalian blood.
Adding additional carbonic acid to your system in sufficient quantities (as in drinking only or primarily carbonated beverages) stresses your lungs they try to decompose the excess.
Don't feel bad about not knowing this, it's new information to me, too. It also explains why I run out of breath walking up 2 flights of stairs after drinking a large soda when I otherwise have excellent stamina and doctors say there is nothing wrong.
I know my platform is no more or less secure than any other
Right. That's denial right there. Dumbass.
You know, Callahan's is a peaceable bar, but if you ask that dog what his favorite formatter is, and he says "roff! roff!", well, I'll just have to...