The BBC has this week been showing some harsh, Afghan combat film, taken by the soldiers themselves in 2007, called Our War and one episode to date. This is available on:

A separate programme touches on this issue of killing. The opening paragraph:
When a soldier kills someone at close quarters, how does it affect them? This most challenging and traumatic part of a soldier's job is often wholly overlooked.

Soldiers kill. It goes with the job, and they do it on our behalf.

But it's an aspect of their work which is widely ignored - even by the soldiers themselves - and this can cause them great psychological difficulty, experts say.
Link to report / summary:

The linked pod-casts are entitled more starkly IMHO 'The Kill Factor' and the sub-title is
Soldiers who have killed in war at close quarters talk about how it affects them today
Link to pod-casts:

I cannot immediately recall a thread on this theme, apologies if there is one.

I am sure many here have read combat histories and books such as John Keegan's 'The Face of Battle' so are familiar with the issues raised.

Apologies for those who cannot access due to copyright reasons some BBC sites.