What would it be about living on board a space ship that would change the passengers so that they would not be subject to discontent, tribalism, revolution, murder, patricide, mass murder, AND MORE!?
These tendencies would have to be suppressed before the space ship is built, before the destination is discovered. Life abroad the starship Enterprise under Picard was peaceful and purposeful because the tendency to discontent, tribalism, revolution, murder, patricide, mass murder (and more) had been trained out of human society. (somehow -- not explained in any of the episodes). And only trained out -- not bred out.
We (humans) do quite well when the stresses of life are well within tolerable limits. Our best traits can come forward and we can behave like Enterprise crew members: rational, reasonably patient, reserved, polite, caring, attending to our duties, etc. It's when stresses are beyond tolerable limits for extended periods of time that we begin to display our very unpleasant potentials.
IF the starship was provisioned with enough space to avoid the chronic stress of over exposure to each other, satisfying amusements, shared strong beliefs in the mission, secure and adequate resources to sustain life, etc. -- sure, I can see it all working out well.
But... the scenario explored in many fictional long space flights is that equipment breaks down, accidents degrade the quality of life, untimely (and natural) deaths of key people, and so forth can bring the whole happy scene to a screeching halt -- just as it has a million times here on this big round starship Earth. (We don't need bizarre viruses, ghastly aliens, or psychopaths to screw things up. All it takes is too many things going wrong.
If there is anything we know for sure, it is that machinery will break down inconveniently, and that the best laid plans of mice and men will eventually go awry.
Adrien Tchaikovsky (Children of Time and its sequel, Children of Ruin) explores some of these problems. A terraforming experiment prepared a raw planet to receive the seeds of earth-ecology. That part worked out well. It's a splendid place. Chimpanzees were to be the most intellectually advanced of species on the planet (no humans). The chimps were to be infected with a virus that would direct the apes to evolve toward much higher intelligence. By chance, the capsule carrying the monkeys crashed and burned, and the virus was released into the pristine environment. Jumping spiders and ants became infected with the virus, and over time (like... 10,000 years) the arthropods evolved into a space faring species--overcoming their natural predatory natures with considerable difficulty.
SCI Fi, of course. Fiction. But it demonstrates my point that one SHOULD know that things can, and probably will, go wrong.
Humans are what we are: primates with all sorts of emotional vulnerabilities capped by remarkable intellect. Both our strengths and weaknesses are deeply established. We are always doomed to a conflict between our equally vital limbic and pre-frontal cortex tendencies.