Getting into the ethical part of the hobby. Is a frog really happy in a tank regardless of size? Maybe he is happy because he is not going to get eaten or maybe he just does not have a point of comparison. I really don't know, but 10 sounds better than 6, it's near 100% larger and I know if my closet was almost double it's size I would be a bit more comfortable. Keep that frog happy
Why are you going there? It has nothing to do with "Ethics"!
You people would love to put more cost and larger quarters for the frog when it just isn't necessary. Frogs don't have the same requirements as Humans or Fish. They do not need as much room period.
The Frog will be just as happy in 6.6 gallons as 10! I've seen Pac-Man frogs live in their entire life and grow to 8" across in a standard 5 gallon bucket.