Robert Crawford - Morality.

Evil itself may be but good disguised,
As many a virtue now was once a vice,
Or held to be such by the moralists;
Or as even in the eyes of foreigners
Our virtues may be vices, theirs to us
As vicious too. We make us new laws still,
And hold that finable and barred to-day
That was but yesterday allowable.
Our neighbours haply no such laws enact,
And privilege what we make punitive.
So right and wrong are still conditional,
And there's no absolute morality
In all the world; for conscience herself is
Full oft but Custom's creature, whom he keeps,
Who sees with him, and hears with him, and acts
As by his power of attorney still.

Robert Crawford

http://www.poemhunter.com/poem/morality-7/