Hmm maybe you didn't read all the great replies in this thread.
Tug cannot 'bring on aggression' unless you have one very very messed up dog. Newfs are very laid back happy dogs.
Tug is a GREAT relationship builder with your dog. I recommend people play tug with puppies, with new dogs, with old dogs etc.
What tug does...
~Teaches the dog an appropriate way to play with humans (so often fixes dogs who grab pant legs etc)
~Tug is a co operative game played by canines in the family group so helps build relationships in a good way.
~Tug teaches boundaries and can be a great way to work on bite inhibition in puppies and older dogs.
~Tug can be a great reward when you want to work your dog in drive when training for competative sports such as agility, obedience, or flyball (hence why its is the first choice of reward by ALL top performance trainers around the world for all breeds)
~Tug can help build hind end muscles when done properly.
~Tug can aid in building confidence in an abused or timid dog.
~Tug can aid in teaching self control to extremely high drive dogs.
That is all I can think of for the moment.
If tug brought on aggression then pretty much all agility and flyball dogs would be very dangerous indeed