Genocide by Omission

I've often wondered what a civilisation would actually look like. I mean a real civilisation, not what passes for one on this planet. One that was comprised of intelligent and capable beings, who actually worked together and were basically decent. What would life be like? How would people act, what would their goals be, what challenges could they possibly have to face?

That is the basis of this story. A great empire spanning galaxies and surviving hundreds of thousands of years, comprised of the kind of people stated above. Is it possible for people to be sane...?