You've reminded me the crap that many abandoned "Born Again" Christians go through when they make the assumption put forward. IE: They honestly believe that all morals come from God and to have no God is to have no morals. When those people have a period of abandonment of their religion/philosophy, they descend into hedonistic excess quite quickly.
Of course, this quickly burns itself out on them (or just burns themselves out) and they come running back to their religion/social group who abandoned them in the first place begging forgiveness. It's especially wierd because until they come back crawling on their hands and knees, the social group often will not lift a finger and activly ostrize the target.