Evan thought maybe they were trained to be that way, since their motto was to be "Swift, Silent, and Deadly". Inside though, he could still tell they were some sort of human, watching many of them cry about their families and being homesick a lot. He started to grow close to each member and they all welcomed him
The main reason that when they came home, they would be scarred for life, is the fact that they had trouble sorting out the threat from the Iraqi civilians. Sometimes, war caused the death of innocent mothers and children, the tearing apart of families by maiming their fathers. Even sometimes marines were injured or even killed, it's hard to tell the difference between everyone in the midst of battle.
When many of the marines came home, they were never the same after being a part of the US army. They get sudden flashbacks and awful memories of people dying in front of them, especially when they caused it. They act cool and all fine in battle because they have to, but inside, war stresses people out and can cause breakdowns. Even Wright was haunted with the amount of deaths he saw, and he was only with them for two weeks, wondering how strong the marines would have to be to have to get through that
Alas, it was time to go home as Evan had everything that he needed already, even though he wanted to stay. From all this, he understood marines a bit more and gained a whole new respect for them, knowing that there were people strong enough and motivated enough to fight for his country like that He commented about how he had a growing admiration of the bravery of the soldiers, how he confidently felt safe in his home country, and how this event would be life changing for him and he wants other to know his amazing experience.