It seems people are overconfident about their moral beliefs. But how should one reason and act if one acknowledges that one is uncertain about morality – not just applied ethics but fundamental moral issues? if you don't know which moral theory is correct?
Philosopher Nick Bostrom discusses moral uncertainty and proposes a parliamentary system to solve the problem.
As discussed in the book Secular Wholeness, a fully functioning and easy to read ethical system is one of the major benefits of religion. The author deals with how to make your own system of ethics, but I found it lacking in the sense that it does not provide terminal values other than the standard, arbitrary, "pick what you want."
Aside from the ability to predict the future (chains of causality - consequences for one's actions), it's been my thinking that the greatest problem of modern day ethics is a lack of discussion around terminal values and how to assign them. Bostrom proposes weighting these values based on their internal feelings and percent of rightness. This seems like a hack that won't work in practice, certainly not for anything that can be applied by normal people. I'm not going to simulate a parliament of ethical values to decide on the rightness of eating ice cream.
But these types of problems are fundamental to determining humanity's future progress, if progress is even a term that makes sense. I don't know what the solution is, but I know that Bostrom is wrong. Hopefully he can come up with something better, after working through the details and realizing "parliament" is a terrible model.