Exactly, the further you can mentally distance yourself from the act the easier it is. Whereas with a rifle, you aim the shot, see the man and pull the trigger, even though your indivdual service weapon doesnt have the nearly potential for death as say a 24 pounder Austrian imported howitzer but its far easier pshycoligically use.

Why is that?

One, you have a small part in a large process, everything from target selection, ranging the target, loading the shell and even lighting the fuze is divided amongst inderviduals, spreading the blame so to speak.

Two, there is nowhere to hide, when shooting a rifle in the loud horror of disorganised combat its very easy to shoot badly on purpose without anyone seeing (or caring) where your rounds hit. Or to simpy do something else, like take cover, or help a wounded friendly or even just leg it.

In a crew you have a job, you do it well or the system breaks down, the fear/pressure of letting down you mates overwhelms the natural unwillingness of killing another human who is not directly threatening you.

The best infanty throughout history relied on this basis to fight together in combat, and really why things like fire in ranks occurred, to bond men together in colective action instead of as a horde of unwilling individuals.

These are the basis of why comanders love crew served weapons or weapon platforms and partly why they are the primary war-fighting systems we use today.