Ethics are not arbitrary. If you do violence to me, that causes me suffering. If you have sex with my husband or my wife without my consent, that's gonna cause me suffering. Both of these things are also highly likely to cause you suffering because most people who are not sociopaths do not enjoy the direct experience of causing someone suffering and suffer guilt for bad actions.
The cycle of suffering is universal to all living things. There's absolutely nothing arbitrary about it.
Don't do things that are shitty to other people does not need a postmodern deconstruction to be understood.