To synthesize from branford and Smokeskin, Basic Biomods removes or blunts the edge of the physiological impact of combat trauma, and VR simulations or XP feeds can help acclimatize the Ego to the purely psychological effects. That being said, witnessing or performing a particularly grisly act of violence is still a situation which can cause a transhuman SV, and you can gain PTSD as a disorder, or have the Combat Paralysis trait. So it's not completely removed, just greatly abated. The only way to completely remove the problem is to use Modified Behavior (which can have its own consequences) or through Hardening. However, transhumans have a lot more efficient back-end for treatment in that regard. Backups offer a very useful post-fact rationalization, Muses are constantly present to allow for psychological reassurance, and simulspace therapy and psychosurgery procedures can take up much less "real time" than normal. Transhumans still have to deal with combat stresses, they're just more efficient at dealing with them. Personally, I would not say that the impact of combat as an actual event is lessened, in the short term. While I've never been in combat, I've heard from several people who have that its one of those situations where you often end up acting much more quickly than you're thinking, and so transhumans would be much relying on instinct as we do today, and experiencing high stress, unless equipped with Endocrine Controls, and only come down and relax after the fact. Similarly, while backups make permanent killing hard to do, for most egos, a violent or painful death is rough on the ego when it comes time to resleeve. Especially if you have experience, most people would understand that, while unlikely to permanently kill the Ego (unless fighting certain bioconservative factions), you're still causing a very significant impact to the enemy which is going to stick with him for a while, so the thought might stick with you for a while. At least long enough for your muse to add it to the list of things you need to have a relaxed chat about before the next sleep cycle.

That article is a fair synopis of Col. Grossman's book The concept of 'distance' from the target is probably important in EP. It is likely that being syntheticaly sleeved would be the single greatest factor in a person's ability to put himself in danger, kill, and shrug off the psychological repercussions.