Why destroy Laketown's bridge?

[Rikae]

Originally Posted by Sauron the White

If Smaug landed on shore, and walked across the big bridge, is it not realistic to expect that he would be met with hostle action from some of the townspeople trying to stop him? And could not that hostile attack also cause the dragon to "misstep" on that bridge and fall into the very water that he is suppose to fear? I think that is reasonable and that was my point.

I really think you overestimate the abilities of a handful of Lakemen - whatever number could fit on the bridge at once - facing toward Smaug's head (and fire).