No he’s not on the fringe. He’s stating a logical fact.
Whether you agree with their beliefs or not, people who believe there is a reward for their actions in life after they die are far more inclined to sacrifice their own life for that reward... be it diving on a grenade to save their friends, or flying a jetliner into a skyscraper.
A person who makes such sacrifice without believing there is a reward, however, could arguably be held to greater honor for selflessness.
But it is not libel of such soldiers, neither past nor present, to state such obvious fact.
As a former soldier, the evos like canine dude are given to hysterical hyperbole as part of their MO. Hardly scientific they are.