Hogwash. 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.
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.
Who the consensus extends to is really the heart of the matter. Most people agree that killing certain people is wrong, but if they disagree on who those certain people are, there's no useful commonality. Some people believe that all killing of others is wrong, some believe that it's okay to kill others under certain circumstances (which can range from a threat to one's life, to petty "dishonor"), and some people historically believed that killing was a necessary duty (e.g. human sacrifice). There is no useful commonality to be had there. You can't appeal to the humanity of someone who doesn't see you as being the same as them, and the restrictions for inclusion as one of them can be arbitrary, broad, and fickle.
By definition, variation is the opposite of consensus.
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.
You seem to believe that there's one consistent set of moral guidelines that separate people into wrong and right camps. This is not true, and most likely never will be true. Instead, there are many competing moral philosophies, many from hundreds or thousands of years ago, that do or don't encourage certain behavior. People tend to pick philosophies, or at the very least act consistently with some set of them, and different people pick or act with different ones.
Vaccines causing autism is simply false though, regardless of any philosophy. It's rather the inverse, much like violence can cause video games.