Why destroy Laketown's bridge?

[The Sixth Wizard]

If this design of a methane-holding bladder in the head is feasible, it would possibly provide two uses: not simply to produce fire, but also to act as ballast, allowing the dragon to fly by his own internal 'hot air balloon'. So the dragon would be forced to employ a balancing act as it were: too much fire production would hinder his flight capabilities, thus necessitating some sort of ground assault.

Let's forget about this methane-bladder theory, please. Dragon's fire, at least in Tolkien, is created through the physical form of the dragon's inner fea, the fire spirit that has been corrupted by Morgoth. Adding in actual bodily elements, while quite interesting, is much too complicated for this thread methinks. I think we should keep it simple for now.

Sorry to completely snub you Bêth...