A law enforcement officer can use whatever reasonable force is necessary to gain compliance with a lawful order. The person in this case was not tased because he was walking his dog, but because he refused a lawful order to stop and identify himself -- and then kept walking after being told to stop. Undoubtedly there's a major investigation about whether this was a reasonable use of force.
A taser is not, primarily, used to cause pain and so gain compliance (though it is darned painful). It incapacitates the muscles such that a person can't move. Their use by police agencies has resulted in a measurable drop in injuries to both officers and suspects when arrests are being made. They are not one step away from using a gun since a gun is only allowed when a level of force is necessary to stop a lethal threat or bodily harm.
Having been at this awhile, I can say that with every new compliance weapon that's come along (mace, CS spray, pepper spray, various baton designs) all -- all -- have been blamed for otherwise unexplained deaths of suspects. What usually turns out to be the case, especially lately, is that a person has so many drugs on board that they were going to die very soon and the officer's actions had little influence on that fact.
Also a note on pain compliance vs. torture. Um, no. When used in the context of gaining compliance to -- once again -- a lawful order, it's one of the allowed tactics to get someone to do something that they are resisting or refusing to do. It could be something like lifting the arm slightly when a suspect is in a wrist lock and is refusing to move where you want them to go. Or pressing behind the ear, causing pain, to get a sitting protester (say) to get up and go with the program. The pain compliance hold should be accompanied by a loud order to do something the officer wants you to do "Walk towards the patrol car." When the person starts complying, the pain control hold is stopped though the person will likely be held such that it can be immediately reapplied.
Of course, in a chaotic situation it's not always textbook, but whatever is happening is almost never torture.
George
