Should a chameleon's life be entirely stress free?
I say no.
My larger chameleons are all free rangers. They have their particular patrol areas, know where the best hunting is, where the fountains are and yes, occasionally encounter one another.
This causes them some stress, they all have fight or flight responses available to them.
I am certain that my chameleons are smarter and more adaptable than your chameleons because of their wide ranges of life experiences.
All of my chameleon keeper friends tell me how healthy my animals are and it's because occasionally they get a little stressed but always have a way to remove themselves from whatever is causing them stress (flight response).
The only time one cham ever inflicted injury to another cham of mine is between a male and female of the same species.
You know what is sick? People who keep their large chams in cages, that's what's sick. That's the worst stress of all and the chams can't do anything about it and die. They can't decide on what temperature they want to bask in, where they want to explore and what to do if they encounter another cham.
I bet you love to keep your chameleons in cages and away from each other, right?