A police force was created to guarantee that the population was under the control of the vaccine. As I don't want to spoil the whole movie, I will leave the description of it as it is now. This kind of feeling inhibition is featured in other places too. In Fallout New Vegas' dlc "Old Worlds Blues" a similar thing is used - a "pacifying field" preventing attacks into the Think Tank.
Philosophy must have some questions about it, concerning mainly free will and the ability to feel as a highway to violence. Enough said, I will leave you some questions: -Are we commanded by our feelings? -Do we have the free will to feel? Or even to control our feelings? -Would violence be condemned if we stopped feeling? -What is more probable to trigger violent actions, feelings or basic instincts, such as hunger and protection?