Having grown up in a house of smokers, and never having smoked myself, I do find it rather callous that the first thing that comes into a smoker's head after killing someone, would be engaging in instant gratification by lighting up.
‘never having smoked myself’
That’s the key point of your posts. Smoking becomes a displacement activity for stress.
“I do find it rather callous that the first thing that comes into a smoker’s head after killing someone, would be engaging in instant gratification by lighting up.”
It’s not about ‘instant gratification’. Cigarettes don’t really get you high, certainly not for longtime smokers. It’s simply a stress management thing.
Someone who never developed that habit probably has other ways of dealing with a very stressful situation, but for a smoker, that’s probably going to be the quickest way for them to get themselves under control.