If emotions are the product of biochemical reactions, then in the future we will be theoretically able to control them. If we could control emotions through technology, should we?
First off, I think that already we can (and do) control our emotions, and we do so all the time. Whenever you swallow your anger or feign joy, to name just a couple common examples, you are controlling your emotions. Controlling our emotions is often a good thing, required by social norms, instilled by social conditioning for the promotion of human harmony. (So I disagree with the premise of the question a little bit...)
Our emotions are like the thermometer for our psychological well being, and although social forces are often used to control them, I believe we need to learn to work with them in a positive way. [^1] If we feel anger, or disappointment, or happiness, or strange, we need to pay attention to these emotions and learn from them.
There is something very important about emotions - they are an important part of being human. For this reason, I think it's not advisable to try to control our emotions so much as work with them, express them in ways that will be positive, and learn from them. Anger is an especially useful emotion, and fear is a big button that is used over and over again for political reasons. We need to understand how these emotions work upon us, for ourselves and for others, in order to be good or become better people.
But the question is more specific:
If we could control emotions through technology, should we?
This could be interpreted to mean that a person would control their own emotions technologically, or that of another, or it could be the control of more than one person (say, a group). I have implied above that we already do this, so we don't really need technology to do so - after all, technology is just the use of tools that can be picked up and used to achieve some goal. Whether it's positive or negative emotions that are being controlled (the word "control" does make it sound like it's the negative emotions we're dealing with, since that is often what we think needs be controlled), I think we already do this at the individual and socio-political level, and having technology to do this would not change my answer.
But. what about the case of the sociopath who doesn't feel empathy, could we cure them through some sort of feeling-machine? If we do so without their consent, them we remove from them their free will and therefore whatever humanity they possess. If it is with their consent, then I think this is a more difficult question. The question then becomes: should individuals be allowed to alter (or control, more specifically) their emotions through technological (i.e., artificial) means? I think it is hard to say no in this case. Our internal lives, including our emotions, are so much of who we are and why we do things, what moves us, that it must be up to us to govern our own emotions by any means that we choose.
Even if we could control (or alter) emotions at the "biochemical" level - that is, before they are even felt by the person my answer would be the same - only if it's the decision of an adult arrived at without them being coerced.
This leads me to perhaps the most common way in which people already do alter (although it's not necessarily to control, so it would be interesting to think about what is the difference here) their emotions or psychic state through artificial, biochemical means - drugs. Licit or illicit, we in the United States and in the western world are really of two minds about this. We are heavily medicated, and at the same time we wage 'wars' on drugs. But that is another debate altogether.
In short, we probably should work to learn from our human emotions, not seek to control them, by whatever means.
[1] You might engage in certain practices, like philosophy, therapy, or meditation, that allow you to examine and learn from your psychic life.