What does the "illusion of safety" mean? Do you think it really helped them feel better about what they were doing?

 

Yes, I believe somehow, the "illusion of safety" helped them (the American soldiers) to move forward, to finish / do the job but not necessarily feel better about it.

Step-by-step explanation

?The Things They Carried tells the story of American soldiers from the Alpha Company and the different, personal, necessary 'things' they carried with them to the Vietnam war. These 'things' were either physical (e.g. guns, knives) or intangible (e.g. Guilt, love). Some of these the men carried with them as a reminder of home, responsibilty and the like, while many were brought simply as necessities as the soldiers went on their missions.

However, in one occasion, O-Brien mentioned about the team taking with them a huge equipment even when it was completely unnecessary, utterly useless, and an additional burden. However, the men did so bring said equipment simply because it was large. And, humans as they were, the burden of a thing gave the men a false sense of safety. That something so big might protect them from bullets or any sort of harm. Thus, "the illusion of safety".