alt Hacker NewsHogwash. We don't even have a consistent set of ethics on how to treat animals today, in the age of the Internet. We have people who refuse to eat meat because of how the animals are treated, and we have places where the locals make sport out of torturing animals to death, and indeed, our own recent history includes that as well (look up badgering).
Not to mention, the variation in treatment of homosexuals (including what constitutes homosexuality), people of different skin colors, handedness, how rape is treated in various cultures (often tied in with notions of property and ownership of all things), or even the various definitions of rape... The list goes on.
Maybe there's a core there in terms of how we treat a given in-group, but equally important is who belongs in that group and why, and that part seems to be tremendously flexible. Ditto for what constitutes acceptable treatment of outsiders.
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You seem to be arguing that the one socially acceptable way to do something is not constant, rather than that moral imperatives truly do change. The reason there are still so many competing philosophies from hundreds or thousands of years ago is because they all more or less make their own kinds of good points to different people or in different situations. That largely doesn't change over time.
One example is the trolley problem and its variations. There's no one correct answer. There are people who believe that interacting with the switch would make you responsible, and there are people who believe that not interacting with the switch when you had the chance would make you responsible. There are other beliefs too, but my point is there's no one single way to view it.
I tend to have a variety of views in general about all things, in part due to being multiple entities (see profile) but also depending on circumstances, rather than sticking to any one philosophy.
That people's beliefs about X vary is not evidence that X itself varies. People have different beliefs about whether vaccines cause autism, but this doesn't mean that sometimes vaccines cause autism and sometimes they don't. Rather, some people are wrong.
Similarly, people have different beliefs about whether it's okay to inflict massive suffering on animals in exchange for some pleasure for us. But this doesn't necessarily mean that sometimes it's okay to do that and sometimes it isn't. It could just be that some people are wrong.
Ditto for other moral issues. It could be that the people who say (e.g.) homosexuality should be punished by death are wrong about this.
That we vary doesn't mean that there is no consensus. There is consensus on many things, and the disagreements we encounter are a source of strife exactly because of the groups that do agree on each side.