I am trying to locate the origin of the expression of "no bad dogs"
("there are no bad dogs, only bad owners"). I know there was a book
titled "No Bad Dogs" written by Barbara Woodhouse, but surely that
isn't the origin.

I'd like a nice history of the expression, including, hopefully, who
first used it, who made it popular, and how it's been mutated/used
over time. (For example, "there are no bad guns.")

The pattern of "There are no bad [something], only bad [something
else]" is quite old. The Greek philosopher Epicurus is credited with
having said "There are no bad pleasures, only bad desires." Various
military men, including Napoleon and General Ulysses S. Grant, are
said to have used the phrase "There are no bad soldiers, only bad
officers." Parenting experts of the 1950s said "There are no bad
children, only bad parents."

It seems likely that the "no bad dogs" saying is a descendant of this
tradition. Barbara Woodhouse certainly popularized it, but I don't
think she can claim to have originated it.

Wow, I had no idea, there were so many expressions!  I entered this
search string for grins:

"there are no bad * only bad *"

...and there are 1,410 results!

Here's a few:

There are no bad foods, only bad eating habits.
There are no bad foods, only bad diets.
There are no bad foods, only bad portions.
There are no bad predictions, only bad timing.
There are no bad soldiers, only bad officers.
There are no bad regiments, only bad colonels.
There are no bad students, only bad teachers.
There are no bad horses, only bad people.
There are no bad talks, only bad coffee. 
There are no bad typefaces, only bad uses of typefaces.
There are no bad openings, only bad players.
There are no bad actors, only bad directors.
There are no bad students, only bad instructors.
There are no bad techniques, only bad timing.
There are no bad birds, only bad falconers.
There are no bad days, only bad moments.
There are no bad markets, only bad deals.

Sheesh!

~~Cynthia

Wow. I had no idea this would be such a monumental undertaking. Thanks
for both of your comments!