Sims behaviors

This game is frustrating me a bit. For one thing, why are Sims so mean to each other when not being controlled? None of my Sims like mischief or pranks, but as soon as I stop giving them commands, the first thing they do is become mischievous to other Sims. They are not being nice to one another and it affects their relationships with friends and family members. The world is a cold, cruel place and I don't want it anywhere in my game. I don't want to totally take away their autonomy, especially in a large household, but if my Sim does not like mischief, why is it the first thing they do when not directed?
Also, is there any way to tone down hysteria? My Sims have emotional control, and yet, the slightest bit of happiness and they become hysterical and die. This is ridiculous. What's the use of giving them traits if they don't work?