Unnatural?

There are two ways you can go about looking at homosexuality from a moral standpoint.  One is non-religious, and one is religious.  Let's start with non-religious.

First and foremost, one should take a look at other animals to determine if homosexuality is unnatural.  Since homo- or bisexual behavior seems to be a nearly (if not completely) universal phenomenon (http://www.physorg.com/news164376975.html), especially true in the case of primates, some of which are completely and universally bisexual, we can rule out  it being unnatural.  As for a morality standpoint, there is little to go by from a non-religious standpoint which doesn't hinge on it being unnatural.  As a method of population control alone, it is useful in and of itself, and worth keeping around with a population of 7,000,000,000+.

Religiously, there are two ways of looking at it, an active diety or a passive diety.  An active diety is easy to rule out, as homosexuality (namely in animals) would not exist in such a scenario.  A passive god(s) would, following any sort of logic, accept a group on their own terms.  If a species evolved which automatically included homosexuality, there would be no immorality in such an act, as long as it was willing (as with any sexual relations).

On a side note, the mere fact that men have a "G-spot" on the prostate, which can only be reached by penetration, proves that homosexuality is natural, and to some degree logical in a social animal.  Dominance would be enforced by "topping" the subordinates, and those which protested least - or liked it - would be more likely to survive for long, passing the trait on to their children.

Just food for thought.