2. By the third or fourth episode, Dr Smith should have been shoved out the airlock or beaten to death with a shovel. Besides his directly threatening the members of the family and getting them into mortal danger. It was blatantly obvious that he intentionally caused the robot's malfunction that stranded them in space to begin with.
It's easy to say "Kill Smith!" when you're not the one who'll have fictional blood on your conscience. Even if Don staged an accident and no one suspected him, he'd have a pretty heavy feeling in his stomach about it from then on.