Mirror in the fishtank

In rec.aquaria.freshwater.cichlids Gill Passman wrote:
: By putting in a mirror you will be causing stress to the fish in
: question...he is now involved in a battle he cannot win...imagine
: spending your entire life face to face with whoever you perceive to be
: the enemy.

I call BS on this one. If this were true, countless breeders around the
world who use rack systems would be subjecting their cichlids to stress
because they can see the fish in the neighboring tank, but not actually
reach them. I watch my N. pulcher and N. similis in neighboring tanks in
the rack stare and flare at each other through the glass all the time.
Are you going to say all of the breeders using these rack setups are
being cruel to our fish? Please, watch for the slippery slope before you
slide on down it.