I believe one of the most important concepts or debates ever to surface throughout the history of psychology is the nature-nurture debate. The debate is about whether a person's behavior and mental state are influenced by society or their family, the way they are nurtured, or if they are a direct result of their genetics, their nature.
Although recently many scientists in the social sciences field have reached an agreement that both nature and nurture are together relevant and important in shaping a person's psyche, there are still debates out there that one is more relevant than the other, or for some aspects of the psyche, one is completely irrelevant compared to the other.
For example, I found an article while surfing the internet one day about homosexuality and how, at one point, it was thought by the American Psychological Association to be a mental disorder. There were various experiments done by various scientists to figure out if homosexuality was influenced by nature or by nurture. It was clear that scientists believed that homosexuality was either nature or nurture; not both. That article can be found here: http://allpsych.com/journal/homosexuality.html
The nature-nurture debate is directly relevant to me because my younger sister is adopted. I have always been interested to see in which ways she has grown up different from me, and in which ways she is the same. She is of the same ethnic background, and was adopted when she was three, but she is still different from me in various ways such as height, body type, metabolism, and interests. She is the same in ways such as speech style and, to some extent, decision-making.
I guess what I still want to know is why the nature-nurture debate still exists to the extent that it does when it has been proven that both nature and nurture affect everything that shapes the human psyche.
You certainly make a good point: Why is the nature-nurture debate still raging in a time when most scientists recognize the importance of both. I can't say for sure; I can only speculate: Because the debate is so old, these two opposing camps are so deeply entrenched that there will always be a debate. But I think another, more important factor is at work. As my professor for abnormal psychology always, said, "etiology dictates treatment." This certainly applies to situations beyond psychological disorders, e.g., criminal behavior. Thus, in order to provide the best treatment, we need to know the underlying cause. It's no use treating a genetic--or predominately genetic--trait or tendency with behavioral approaches; conversely, you can't expect to make much ground with biological interventions when a trait is determined primarily by the environment. Thus, only by better understanding how each of nature and nurture contribute to a given trait, disorder, etc., can we hope to provide the appropriate treatment or intervention.
In summary, yes, the distinction between nature and nurture is important. Still, the question remains: Why the intense divide between the two, the raging debate between the camps? I think that's fizzling out, but it takes time to get rid of opinions, debates, and rivalries that are so deeply entrenched.