Romulans have an Empire which straddles half the beta quadrant.
The Vulcans can barely full up one planet.
Rampant emotions lead to nuclear war my ass.
It's all about resources.
Too many people not enough shit.
Controlling emotion is about removing the sex urge, shrinking the population and creating the necessary excess utility required to fund a utopia, thus assuring the end of war and the survival of the species.
It's all really obvious if you just take a second to think about it.