Americans cannot step in for every injustice all over the world. As long as what is happening is not a threat to Americans, it is not the Americans' place to step in and try to control it. We are too extended around the world as it is. There is also no way to choose when to step in and when not to, and it becomes political.
The United States is a world leader in many ways, but should not be the world's police force or moral compass. There are ways the United States can make efforts to improve the lives of oppressed people globally without direct intervention. Many other countries of equal economic success to the U.S. are not actively involved in managing other countries.
Human rights atrocities happen globally everyday, many of which can be solved without the use of force and which the United States never even considers intervening in. The broad concept that the US needs to be the world's police is completely counter to the Founding Fathers' vision for our country, and puts undue economic ( and mortal) strain on our country without directly benefiting us at all. Americans would do better to protest peacefully and engage in an economic embargo, rather than sending troops.
No, the U.S. should not step in to protect Philipino activists yet. The U.S. can't just jump in every time there is a disturbance around the world. We have to step back and let others solve some of their own problems. However, the U.S. also has an interest in human rights around the globe, so at some point it may become necessary to intervene.