> What is today a moral imperative is not the same as what was moral 50/100 years ago

This is absolutely not true, and I would strongly suggest taking an ethics course. One of the most fascinating realities of the human condition is that it does seem that moral imperatives tend to be constant, the most obvious of which is the Golden Rule (which is at least 3000 years old), but there are many (the Ten Commandments or Hammurabi's Code are good jumping off points).

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.

I think its more accurate to say where you find consensus in morality, e.g. murder is wrong outside authorized violence (e.g. war or policing), you also find extensive selective pressure behind this behavior. It makes sense that all collective society cultures would outlaw murder; such a behavior is incompatible with collective living behavior whether you are in a cave or a modern skyscraper. Early societies have always been rejecting those alleles from their gene pool.

When you find shades of grey and great spectrum of opinions across time or space, its more that there isn't a strong selective pressure either way. How people are expected to dress is a good example of this. This has no real affect on society behavior or fecundity, so you see a spectrum of opinions that explain the differences between what you see in the middle east and a beach in brazil.

I did a philosophy minor, one class of which was the philosophy of ethics. There are many rules that definitely are not ethical today even if they were in the past so I don't think the point you're making really holds. Hammurabi (an eye for an eye) is probably one of the worst examples you could have cited.

Did the Golden Rule apply to women, gays, and slaves over the last 3000 years?

The definition of moral imperative is "an ethical principle, rule, or action that is strongly felt, urgent, and required because it is morally right." The Golden Rule is clearly not a strongly felt part of the human condition, or it would not be so ignored over ages and continents.

You take a class. Do you think coveting is immoral? Retributive justice? Human sacrifice?

Seriously. This idea that humanity has not spent millennia analyzing these concepts is pervasive in the modern world, and the only thing I can think to attribute it to is a lack of education. Not because I want to be insensitive, but because as soon as you start absorbing material and integrating the real timeline, you can't unsee it.

Is hammurabi's code moral? I don't know if I think that someone who takes out a person's eye deserves to have their own eye taken out also

It's not the case that all aspects are constant. There's some common themes across cultures and times, but it's definitely not the case that the morality of ancient people was the same as today.