If the PCs have been in enough battles, they will certainly gain a list of Things We Don’t Talk About.
I’m not sure how you roleplay heavy ghosts and bad dreams, but they’re out there. A sufficiently heavy load of guilt could well lead to some nasty self-destructive behaviour: but even a lighter load – cleaning up the remains of your dead comrades, knowing that you gave the order that lost half the company, or even just survivor’s guilt – is going to take some doing to get past.
Traveller is primarily a military SF game: but by and large, I’m staying in exploration, culture and politics (with a dab of technology here and there).
I have my reasons.