Are all moral or ethical standards subjective? That is, are they constantly changing with changes in times, cultures or religious beliefs?
Although we cannot speak for what will occur in the future, so far it does not appear that there are any moral or ethical standards that are absolute. We can see moral and ethical standards changing over time even within fairly similar cultures.
For example, let us look at the evolution of morals and ethics in our own society. The United States has always been a Western culture which has been deeply influenced by Judeo-Christian ideals and by the Enlightenment. Even so, our morals and ethics have changed dramatically over the years. For example, we once felt that it was perfectly moral to enslave African Americans. We later felt that it was acceptable to segregate them. In both cases, people used the Bible to justify these actions. Now, we find both practices abhorrent. We once felt that it was moral and ethical to take land from the Native Americans, often by violence. We felt that it was legitimate to go to war with Mexico and to then take half of their national territory. We would not do those things today.
When such basic moral and ethical issues as when it is right to kill or steal or enslave can change over time, it seems that all moral and ethical standards are subjective.