In the final chapter of The Great Gatsby, Nick Carraway speaks of Tom and Daisy Buchanan in these words
"They were careless people, Tom and Daisy - they smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made..."
He calls them careless people and in that accusation lies Nick's great disillusionment with just about everyone he has met since coming East, except for Gatsby of course.
Everything about the superficial and shallow people he encountered strikes him as "careless" and he can no longer tolerate the values, or lack thereof, of the rich and fashionable set, to which the Buchanans and Jordan belong, nor can he excuse the crass behavior of the social climbers who populated Gatsby's parties.
Nick sees himself as separate and different. His values of friendship and loyalty are in sharp contrast to the indifference and uncaring attitudes of so many others, including Daisy and Tom. At heart, Nick recognizes that he cannot remain where people like Daisy and Tom carelessly and callously destroy peoples’ lives, shield themselves from the consequences of their actions with their money, and leave others to deal with the fallout. Nick represents the traditional values of the West, whereas Tom and Daisy represent the moral decay of the East. That is why, in the end, Nick leaves New York and returns to the West. Therefore, we can say that he is not guilty of being careless, like the Buchanans.