Yes, they do munch on nightshade plants, but for healthy tomatoes after the munched areas grow new branches. Also, the hawkmoth adult hovers at deep throated flowers to drink nectar which in turn gets pollen grains deep inside, most animals cannot pollinate that deep so they serve a purpose actually. Unlucky moths get eaten by bats.
Video -
http://youtu.be/1xizHcWpBpI
