Emotions embody traditional knowledge which we don't have a full, conscious understanding of. Emotions are also fallible and possible to change.
If we feel good or bad about something, we might be mistaken. But it's not irrelevant. There is, in general, some reason the tradition causes people to have that emotion in that situation. When in doubt, it's better to use traditional knowledge, which has been criticized and improved a lot, than to make something new up from scratch.
Here is a rational way to use emotions in argument: "If doing that would be good, why do I feel bad about it? Do I have any ideas to change it slightly so that I'll feel good about it? If there is no way to change it to be more emotionally appealing, why isn't there?" This doesn't assume the emotion is true.
This argument notes the violation of the traditional knowledge behind the emotion and uses that as a criticism. Any idea which violates an emotion needs to have an answer to this kind of questioning and criticism. If there's no answer that's bad; if you have a good answer then it's OK.
Here are two ways to resolve emotional conflicts. First, if following an emotion would cause a problem, then you shouldn't want that. That's a good reason to change your mind and look for an unproblematic alternative (possibly a different way of following the emotion, or not). Second, if you have extensive knowledge about the issue and have a really good idea, which you've scrutinized extensively, you could be happy to try it (and not conflicted).
Sometimes we find our emotions are unhelpful or cause problems in a repetitive way. In those cases, it's important to change our emotional makeup so that stops happening.
Sometimes we find we make decisions while emotional and regret them later. This is a flaw, but we can improve and fix it.
Sometimes people get angry and then they assume that if they are angry the other guy must have done something to make them angry. They take their anger as justification of their own anger, which is invalid. Worse, some people believe they had no choice but to be angry. It's not their decision, it's just anger which is a natural, biological force. Thus they bear no responsibility for their anger, only the victim of their rage is to be blamed.
Can We Change Emotions?
Some people are pessimistic about their ability to change their emotions. They think that emotions are biological or natural, and that emotions aren't ideas, knowledge or traditions. They think it follows that emotions can't be changed anymore than we can change our hair color.
Of course, although hair color is genetically determined we can change it: it just takes dye. Similarly, if one is born without legs that is a big problem. But it's also a changeable, improvable situation. One can get prosthetic legs or a wheel chair. Genetic causes do not mean we're helpless.
In general, genetically determined problems are actually easier to deal with than problems of knowledge and ideas because they are a fixed target. Genetically determined problems don't change or get harder over time. They have a limited amount of complexity and only need to be solved once and they stay solved.
When it comes to ideas, things can be harder. Sometimes we unconsciously use creativity to maintain our current personality. Trying to change it may not just involve working against a static obstacle. It may be an adaptable obstacle that tries to avoid being changed.
In any case, nature or nurture, there is no reason for pessimism. There are reasons why we can expect to be effective at changing our emotional makeup, our passions, and our habits, if we make an effort. Here are some reasons:
Many people think sexual lust as something they have almost no hope to change because they can't imagine being in control of it (compared to, say, getting angry, sad or happy, which they know that sometimes people manage to have some control over). But William Godwin explained that sexual lust is a matter of ideas that we can make choices about. He pointed out that sexual pleasure is actually fragile — people will go to great lengths to avoid being disturbed because it ruins the pleasure and they "lose the mood" (in modern terminology). He also pointed out that if someone is having sex, and as immersed in that experience as can be, he will still forget about it and sober up, in seconds, if you just inform him that his father has died, or anything he considers significantly more important than sex. He will stop in the middle if his reason tells him something else matters more.
While sexual lust is a fragile thing, easily defeated by reason, most emotions are much more so. People will stop being angry if they see clearly that they were in the wrong (I don't mean you give them what you consider to be a decisive argument, but rather what they consider a decisive argument so that in their own opinion they were clearly in the wrong.) Happiness is fragile if you just tell someone about a sad event. Sadness is fragile if you inform someone that they won the lottery.
People sometimes make changes in their life — such as becoming more optimistic or becoming a Christian — and then find they are happier more often. That is another well known example of taking control and changing one's emotional personality.
Some people say they aren't responsible for emotions, and have no control over them, because they are scared of taking responsibility and failing. But the truth about whether our emotions can be changed does not depend on how much we'd like to dodge responsibility.
Emotions, genetic or not, must go through multiple layers of interpretation before they are meaningful to complex, high-level world views. Whatever the origin, the final result, as manifested in human behavior, is going through some layers of interpreting in one's mind. That means that even if the initial emotion is never changed, how one interprets it, reacts to it and uses it can all be changed within one's mind.
Consider drunk people. They often claim the alcohol gives them a new personality. That's ridiculous. Beer doesn't have much information in it. The new way of acting was already in the person himself and all the beer could have done was activate it in some way. In fact, people sometimes take on their drunk personality without actually drinking — beer isn't necessary to activate it. This illustrates that significant changes in demeanor are not only possible but commonplace.
How To Change Emotions
Here is my advice about how to change one's emotional makeup:
First, be calm. Take your time, there isn't as much rush or pressure as it feels like. Emotional reactions are often immediate. Instead, act thoughtfully and slowly; think things through; don't react until you're ready.
Second, be self-aware. Pay attention to, and keep track of, what you do and think and feel, and compare it to your values and how you want to be. Whenever it doesn't match, then think about what would match and at least form a quick guess at how to do better next time. Replay conversations and events in your head and look for things you could have done better, and things you wish you hadn't done. Look for emotions you felt, and any problems they caused. You can also look for emotions you didn't feel but would have liked to. Don't worry too much about changing; just notice everything, pay attention, and form some ideas about what'd be better and guesses at how to do it, and try imagining yourself acting in the new way.
With practice you'll learn to notice things faster. Instead of hours later while reflecting, you'll notice minutes later. You'll have ideas what to do better, and spot things you wish you didn't do or feel. Then with more skill, you'll start to notice in seconds.
If you can notice within seconds, and you act and feel slowly, you'll be able to notice before you've done or felt anything. Then you can do something else! Now you have better control over your life.
That is great progress. But it's not the end of the journey. Now you can think of new policies for how to live, and how to react to things, and you can actually try them out to see how they work. And many won't be great, but a few will be improvements. Now you're learning. You're conjecturing how to live better, and trying out the conjectures. You can also consider your conjectures critically, that way if you notice a problem with one you won't have to try it out. Over time, the old bad habits and emotional reactions that you didn't want will fade with disuse, and new ones will form as you find ways of acting that you don't see anything wrong with.
None of this is disrespectful to emotions. It doesn't assume they are all wrong, or worthless, or don't contain knowledge. It's the same sort of approach one should take to ideas in general: criticize their flaws, conjecture ways to improve them, and gradually move forward. Sometimes people go wrong by trying to ignore their emotions without replacing them. People sometimes do the same thing with ideas. This doesn't work because we have ideas and emotions for a reason. They solve some problem. At the least, a certain emotional reaction gives guidance about what to do in a certain category of situation. Some replacement is needed which solves the same problem by giving you an idea of what to do instead in those situations.
For another perspective on emotions, see Bounded and Unbounded Emotions.