If it feels good for me isn't it right?
Feelings are not reliable. They can change. They can be dangerous. For example, the feeling of anger produces numerous ills, including murder.
As explained by Herman J. Eckelmann (Montgomery book in the resource list), people have felt good about "bad" systems as well as "good" ones. Nazism, communism, and the cult of Jim Jones all began with good feelings.
These examples show that the notion that truth is relative to the cultural setting or situation is a cop-out. While there may some differences at the margin from culture to culture, every culture has essentially the same set of moral absolutes. For example—trustworthiness, loyalty, honor, self-sacrifice, etc. are common to all cultures. And when a culture violates moral absolutes, we rightfully condemn such activity. What "is" is not equivalent to "what ought to be." Ritual human sacrifice is never right no matter what the culture. The difference between Adolph Hitler and Mother Theresa is not simply cultural. There are standards.
Utilitarianism or majority rule are likewise inadequate standards for truth. Slavery in America was not right just because it was normal or useful. There is transcendent moral truth.
We do not speak of morals in animals—only in man. This enlightens us to the biblical teaching that man is "made in the image of God." As put by R. C. Sproul, "man's role as image bearer of God carries with it an awesome moral responsibility that cannot be neutralized by a relative standard of goodness."
Being a Christian does not make us perfect. But history suggests that by removing the restraints of God's law and love, the worst barbarism breaks forth. Which philosophy produces love: every man for himself or Christian compassion?
Sinful man tends to give preference to models that rationalize his lawlessness and desire for absolute self-sovereignty (what feels right), rather than on the basis of a transcendent moral order that enables the human soul. The goal is truth, not excuse.