Goats can symbolize virility, but because goats are promiscuous, they have been symbols of licentiousness. The goat is also the player on the team that makes a mistake and costs his team the match--the opposite of the hero. Sheep follow blindly, and are seen as timid. C.Y. Leung, Hong Kong's chief executive, was widely derided for calling on Hong Kong people to be sheep in the year of the sheep. So "ram" seems like a good substitute. But when Americans say "ram," they are thinking of the male bighorn sheep; it is a different species of sheep, but it is still just a male sheep; the female is a ewe. So it is not appropriate to say "year of the ram," as Chinese University's Art Museum among many others has done, because it excludes females.
Of course, this is only an issue in English; in Chinese the word yang 羊 includes both goats 山羊 (literally "mountain yang") and sheep 綿羊 (literally "wool yang"). Some scholars (see NY Times article here, for example) have noted that since goats were more common in northern China, while sheep were raised in the south, the original horoscope yang probably referred to a goat.
Goats and sheep are actually different genera, not just different species; they even have different numbers of chromosomes. But that does not mean every culture will name them differently; there are plenty of animals that are lumped together or distinguished as separate without regard to the linnaean taxonomy. I suspect the reason Chinese uses a common word yang for both genera is that in traditional China, goats and sheep seem to have been raised in different parts of the country, so it was not necessary to distinguish clearly between them.
This is just an example of differences in what anthropologists call cultural domains. Different cultures divide the world in different ways. Many cultures do not make a clear distinction between the colors green and blue, using a word sometimes translated as "grue" to describe the two together. Taiwanese Hokkien uses 青 to describe both green and blue; this would sometimes confuse me when native Taiwanese speakers, while speaking in Mandarin, would point to something "obviously green" 綠 and call it "藍 blue."
It is laughable, then, that the folklorist Zhao Shu of the Beijing Institute of Culture and History tries to take this quirk of taxonomic difference and make out of it a general principle of Eastern v Western mentalities. The NY Times articles says:
He also drew a lesson about the virtues of Chinese tradition. “In Western culture, things are subdivided into more and more detailed categories, and that’s why Europe has still not been unified after so many years,” he continued. “If you want to say whether it’s goat or sheep, then why not also ask whether it’s a ewe or a ram? But Chinese culture has an inclusive spirit and stresses harmony.”A wonderful "just so story," essentializing "the Chinese" as harmonious and inclusive. All revolutions and wars are wiped out as anomalies. Factionalism, also often seen as characteristic of China, gets wiped out by "Chinese inclusiveness." The fact that "rice" in Chinese can be 米 (polished rice) or 稻 (husked rice) or 飯 (cooked rice) but is only "rice" in English is ignored. It seems these ridiculous cultural generalizations will never be overcome. They are too comforting. And amusing.