The part where you said they were to be taken at a young age, trained exclusively for the purpose of combat, and kept away from politics, economics, culture and religion. Even if they could theoretically quit, what kind of life they could have outside of the circus with that kind of background? One choice is no choice. And no choice is slavery.
You assume too much. The word I used was CHOSEN, not taken. Where I come form, just because you have been chosen by a certain college does not mean you are absolutely bound to attend it.
Also, I said this group will be outside the influence of politics, economics, culture, and religion. Meaning that they can't be bribed or coerced or biased into throwing a fight. Otherwise, this system will not work.
Now, if you would, please stop putting word in my mouth (sort of) and actually make a suggestion on how you would make this ritualistic combat system work.