They can be, but they are then subject to a change in societal ethics over the course of time <.<

Eg. 'It's immoral to be homosexual' used to be considered a legitimate argument in the 1950s say, but nowadays you'll probably just be laughed at for saying something like that.

Then you have the more unchanging ethics, like Killing people/Stealing which have been recognised as generally wrong since societies started to form. An argument over whether it is right or wrong to kill another person would generally be led by the ethical stance of 'it's wrong because it harms others' >.>