No matter what they did, both Decker and Tracey lost their crews to unforeseen consequences. They were both traumatized by their circumstances. Decker was unhinged, and so was Tracey. If the circumstances were swapped, who knows how Tracey would've reacted to the planetkiller or how Decker would've reacted to Omega IV and its seeming potential for humanoid immortality?
Starship captains go crazy sometimes. It is likely a hazard of the personality types that strive for starship command in the first place.