There is nothing to get humanity to lose it sh*t then to have tons of crises. After a few mere decades from the numerous essential crises that Mankind has to endure (First Contact, the Post Atomic Horror, the Genetic War, the Klingon War, the Romulan War) and the technology to end scarcity of essentials the people in Star Trek TOS would seem to be a little corny to us. They are optimists not because they are hippies or corny but because they future is still full of brand new awesome compared to the nearly two centuries of absolute murder, mayhem, and confusion. You see a change in Star Trek TNG, where they don't know anything different but having everyone's basic needs provided, except on colonies that went straight to hell.