Knowledge is one thing, truth is another; to mistake the two is a grievous error. "Situation ethics" is a euphemism of this Brave New World of fashionable sin, and hedonism. Wrong is forever wrong. Right is forever right, and the twain shall never meet.
In general terms, ethical relativism is a bad idea, for there is no clear, unmoving standard of right/wrong, acceptable/unacceptable, or whatever other pairing you might use. The possible consequences of such a system both for an individual and a community are dire. As soon as the word "global" is interjected into the conversation, however, relativism almost becomes necessary in order to satisfy the varying standards of acceptable conduct.