My own opinion is that every man with a pair of pants on, should have a knife in a pocket. Everyman, no matter what his profession or occupation.
As for soldiers, they do need a knife, but how much knife is open for debate. I spent a wee bit over 10 years in the army, and was going for a 20 when I was medically discharged because of injuries received while serving. I spent my time in the engineers, and it was basically like working for a contractor. Our mission was construction and building. So everyday was a day working on a construction site. A pocket knife was a needed thing. Line to b cut for surveying stakes, cutting open burlap bags of materials and hardware, sharpening sticks to serve as survey stakes, opening c-rat boxes, strip wire for connections, and a zillion other uses. It was apparently enough of a necessity that our supply room kept both the Camillus TL-29 and the ML-K scout knife, sometimes called the demo knife, on hand.
But in the bit over a decade I served, I can't ever recall one time I needed anymore knife than whatever pocket knife I had on me. Hopefully a SAK or scout knife type of thing with a few tools on it. This is including a tour in a little Asian country called Vietnam. In general, soldiers and sailors are just like the general population. Most are not knife people who obsess over what knife to carry that day. In 99% of the time, whatever the supply room issues is good enough. For the few that are the afflicted and obsessed knife knuts, they will just go buy what they want.
For the modern day soldier, a basic multitool or scout knife will do very well. A SAK is always a good thing.