>> I mean you can find tons of animals that exhibit in same-sex behavior.<<
Yes, because most animals engage in sexual behavior simply as a result of environmental stimuli. For instance, most animals simply go into periodic "heat," where they are sexually aroused by what time it is in a sexual cycle, and not by the characteristics of another animal present. Such animals often mate with members of the opposite sex only because they find members of their own sex unreceptive. A cat in heat will becom esexually active with whatever fits its anatomy the best. A same-sex relation is better to a cat than a carpet, but a carpet will do, also. But that same cat will, AFAIK, always prefer another cat of the opposite gender.
Humans are very unique among animals in that our sexuality is not cyclical. Human female's breasts are perpetually enlarged for sexuality, and both genders are capable of sexual relations at any time. Rather, human sexuality is mostly triggered by psychological, rather than physiological conditions. (There are some vestigal physiological causes; Men tend to be visually stimulated while women tend to show a circilunar greater ease of arousal.) The complex psychological elements of sexuality are altogether absent in most animals, and therefore comparisons to human sexuality are just silly.
I would have a couple conditions before I would consider relating animal homosexuality to human homosexuality:
1. The animal would have monogamous in nature. This is not because I am asserting that humans are monogamous in nature, but because it establishes sexual psychology, not simply indiscriminate humping; In corollary, the animal would have to be exclusively homosexual; bisexuality in animals would only demonstrate a lack of cognitive discrimination.
2. The animal would have to have heterosexual opportunity. In other words, I wouldn't classify as homosexual animals which are striving for heterosexual matings, but which are physiologically compelled to sexually climax in spite of the ability to find an appropriate mate.
Now I wonder what kind of "sexuality" it is when my neighbor's dog tries to do my leg. If it's a male dog on a man's leg is the dog homosexual? But a male dog on a woman's leg is heterosexual?...
It's pointless to discuss these types of things with the homosexual lobby. They have no argument other than emotion.