Homosexuality is considered by many to be fully natural. To prove this point, examples of homosexual behavior in nature are often cited because animals do not reason as we do. But if they do it, it cannot be considered wrong for humans to participate it. In fact, denying that certain humans are homosexual is denying part of nature and denying that we, humans, are another species on Earth. Different developmental studies are often cited that show that homosexuals and heterosexuals differ in genetics, prental neurohormonal levels, response to pheromones, and brain structures. These all attempt to show that the orientation is something that cannot be controlled or influenced by the environment. This acts to seperate behavior from disposition towards behavior. This is a valid approach however, bcause accepting one's determined orientation is to accept the behaviors that flow from this. I know I will recieve criticism from people citing criminal examples (e.g. someone predisposed to violence), but this question is not the purpose of this post so it holds little sway in the argument.
When people consider homosexuality to be unnatural, they focus on the behaviors associated with homosexuality, and completely ignore the underlying orientation. To back of this claim "ex-gays" are often cited as examples where someone partook in homosexual behaviors at one point, but through conversion therapy changed. Again, there are many criticisms of this fact, but it is not pertinent to the post. Additionally, this side states that homosexuality is against nature because it does not allow for reproduction and the passing on of genetic material to subsequent generations. As such, homosexuality is deemed to be unnatural.
The debate over the origins of homosexuality comes from the need to have a valid reason for discrimination or thinking less of homosexuals. The only valid reason for this would be that homosexuality is a conscious choice by the individual. The free will of the individual must play a role in their homosexual behaviors. If homosexuality is a conscious choice, then the act itself can be deemed to be moral or immoral and right or wrong. This distinction lies in contrast to an act being determined or coerced. If an outside source influences the actions of an individual, it becomes bery difficult to assign responsibility and impose limitations. Some examples of this are a man pulls your finger on the trigger of a gun and kills someone or you are attacked and killed a man in self defense. In either case, it is incredibly difficult to assign responsibility for the death of another to the individual because the individual lacked completely free will. By stating that homosexuality is a choice, the actions of a homosexual in same sex relations can be judged easily. In being able to judge the actions of a homosexual, rules and laws can be ethically passed that control them because they are solely based on the conscious choices made by the individual. Homosexuality becomes something little different than robbing a bank. The individual who robbed the bank chose to rob the bank. He was not forced or coerced, so is able to be held accountable by the law for the action. The homosexual chose his behaviors so can be restricted by law the same as another individual who has chosen a behavior deemed wrong by society.
If homosexuality was natural or fully determined it would be impossible to ethically pass laws restricting its practice, acceptance, or equality because the individuals would have no responsibility for their homosexuality and such, could not be held accountable for it. It would become something little different than passing laws against an individual because the individual's gender or race. An individuals gender or race is determined so cannot be discriminated against because the individual did not act freely to be that way. Additionally, any restriction on homosexuality would likewise not be ethical if homosexuality is natural because it would punish the individual for being different. Any restriction would act to restrict the individual's liberty to act out their nature, or imposing a restriction on the individual's free will (free will here in a Humian sense).
The question of whether or not homosexuality is natural is a question of whether or not it can be constricted like other conscious choices. Is homosexuality closer to race and gender or acting asocially through things like robbing a bank? By ignoring the orientation and focusing on the free will of the behavior, the people who view homosexuality as unnatural say that it can be restricted ethically. By looking at homosexuality as the determined orientation and the behavior as only a result of it, the people who view homosexuality as natural say that it cannot be restricted ethically.
To try to combine these two views makes the question rather difficult: behavior as a choice and orientation as determined. However, the conclsuion is one that would support the view that homosexuality cannot be restricted ethically. The orientation determines the individual's behavior. It is the innate attraction to homosexual or heterosexual partners that lead to the behaviors. Here, the behaviors become choices, but not freely determined choices. If an individual was forced to fire a gun and kill another individual, the individual is not held responsible for the death. Much in the same way, the orientation of the individual is forcing the behavior so the individual cannot be held responsible for the actions. In this light homosexuality behavior cannot be seen as a choice and so cannot be considered as the responsibility of the individual. So homosexuality should not be restricted or judged. Despite this, the behavior can be resisted, but resisting does not change the underlying nature of the individual. A homosexual does not have to engage in homosexual behaviors. However, he would still retain the homosexual orientation. But the choice here is not one that is truly and completely free. The individual can choose to resist his or her determined nature or to realize his or her determined nature. That is a choice up to the individual, but it is suggested that it is a forced choice and cannot be judged as harshly as other, completely free choices. The individual had no control over the events that led up to the necessity of the choice. Having to choose is a matter of situational or dispositional luck and therefore judgments on this have little to no moral responsibility. So, restrictions cannot be placed on the individual, whether he chooses to be a homosexual or a heterosexual behaviorally, because the necessity to make the decision to act or not act was out of the individuals control. So, in these two different conbinations, we see the same end results, the homosexual cannot be held accountable and responsible for his or her homosexual behaviors so cannot be restricted by the law.