Yeah, Cosmos is by Sagan as well. He is a great author. And I think the TV Series came out first, which was hosted by Sagan, then he wrote the book at around the same time.
I don't know a lot to be able to make a good estimate of what they would look like...but I suppose if I had to guess I'd probably say they would be somewhat like us.
I don't think I would say they have a chance of destroying themselves unless they're population was as big as ours because I have seen that the more people there are, like in LA or New York City, the more annoyed and frustrated people are. I live in a small town and people are waaay less annoyed here. When I go to a bigger city I can feel the difference. Or maybe if their planet was much bigger than ours...
Do you think this would make a difference?