I personally think that spark itself is a kind of mind control. And this assume makes the locket's function clear: denial of mind effect.
And possible reason for doing it :
Somebody found a intelligence enhancer, but it makes subject's mind unstable as a side effect.
War is considered bring technologycal advence, but they don't want to hurt themselves. So, they make war at somewhere else.
And inject sparks to people there, it will excel the tech advence and easily make war due to unstable mind.
And the 'someone' take techs from them and keep themself safe and uneffected.