In Star Trek Into Darkness, Spock claims he can choose whether or not to feel an emotion. He makes a good case that in certain situations feelings would not functionally help him and that resisting feelings would spare him from suffering. The always emotionally charged Captain Kirk asks Spock how he does it, claiming that he himself cannot.
So the natural question is: Can humans chose how to feel or is this simply a Vulcan thing?
The answer is that people can often act in a Vulcan manner and choose their feelings.
In many cases we do not wish to feel certain emotions. For instance, when watching a commercial about the mass sufferings of others, one may not want to feel compassion and sadness, and instead simply enjoy the comedy program they are watching. Researcher Daryl Cameron and colleagues find that in these situations, people can "go cold" and turn off their empathy. As Daryl Cameron writes, you "can choose to feel more compassion."
Additionally, meditation and mindfulness are all practices that can teach people to calm their emotions. People can develop the ability and skills to stop (or reduce) themselves from feeling certain intense emotions. Daryl Cameron also finds that people with higher empathy regulation can turn it off more easily in specific situations.
People can also choose to feel something more intensely, not just less. Sometimes we may want to feel certain emotions. We may want to feel angry before a competition, feel sad before volunteering for a charity, or feel disappointed with ourselves in order to motivate ourselves. People can both psychologically and behaviorally lead themselves to take on these emotions, e.g. by exposing themselves to different warm up music like a violent (or calm) set of songs.
However, emotions cannot always be chosen. People have immediate emotional reactions. These emotions may be consciously re-appraised, but some emotions may be too powerful to overcome. Furthermore, some emotions may operate unconsciously.
Thus, although people have some autonomous control over their emotions, they are not robots. No matter how well humans can control their emotions, like the half-human Spock in the new Star Trek films, nearly all humans can become emotionally compromised.
So is the ability to choose your feelings a good thing? In the end, to live a successful and happy life, a person needs to be both the unfeeling Vulcan and the feeling human. This means knowing when one should choose not to feel and when one should let their emotions run wild. Star Trek Into Darkness provides a good commentary on the difficulty of this balancing act and how it complicates issues of friendship, revenge, and rational action.