I don't think most people living in other times & places privately agreed with their society's public morality, to the same extent that we do today.
For most of history (not prehistory), there was no option for public debate or even for openly stating opinions. Morality was normally handed down from above, from the rulers, as part of a religion. If those people had an opportunity to live in our society and be acclimatized to it, many of them may have preferred our morality. I don't believe the reverse is true, however.
This doesn't prove that our morality is objectively better - it's impossible to prove this, by definition - but it does dismiss the implication of the argument that "you like today's morality because you live today". Only the people who live today are likely to like their time's morality.
In the middle ages in Europe the middle class lived after much stricter morality than the ruling class when it comes to question such as having sex.
Morality was often the way of the powerless to feel like they are better than the ruling class.
In this video, Julian Savulescu from the Uehiro centre for Practical Ethics argues that human beings are "Unfit for the future" - that radical technological advance, liberal democracy and human nature will combine to make the 21st century the century of global catastropes, perpetrated by terrorists and psychopaths, with tools such as engineered viruses. He goes on to argue that enhanced intelligence and a reduced urge to violence and defection in large commons problems could be achieved using science, and may be a way out for humanity.
Skip to 1:30 to avoid the tedious introduction
Genetically enhance humanity or face extinction - PART 1 from Ethics of the New Biosciences on Vimeo.
Genetically enhance humanity or face extinction - PART 2 from Ethics of the New Biosciences on Vimeo.
Well, I have already said something rather like this. Perhaps this really is a good idea, more important, even, than coding a friendly AI? AI timelines where super-smart AI doesn't get invented until 2060+ would leave enough room for human intelligence enhancement to happen and have an effect. When I collected some SIAI volunteers' opinions on this, most thought that there was a very significant chance that super-smart AI will arrive sooner than that, though.
A large portion of the video consists of pointing out the very strong scientific case that our behavior is a result of the way our brains are structured, and that this means that changes in our behavior are the result of changes in the way our brains are wired.