I think you'll find the Japanese consider China's intent to wrest control of the Senkakus from Japan's administrative control as an aggressive act... or do you consider Japan to be "on the other side of the planet" from China? The U.S. considers it aggressive (to the extent the Obama administration has a coherent foreign policy which can be differentiated from abject appeasement at least) because it has important strategic allies in the area, namely Japan, South Korea, Taiwan, the Philippines and other Southeast Asian nations. In economic terms China is also an important trading partner to the U.S., and anything which destabilizes the area, or interferes with the flow of trade will impact this partnership to the detriment of both. And lastly, the U.S. has a possession in the area (i.e. Guam), not to mention its treaty obligations to assist the Japanese from outside threats.
Failure to recognize these and to take them into account, while may be good from a "rose colored glasses" perspective, is nonetheless both naive and ignorant.