Well, if you're a Berserk fan, Logic would state that it's the Woman's job to warm a Man in times of Illness or Great Injury...AND she has to be Naked, or else this method of healing won't work. (Almost makes me wish I lived in that time frame). From what I've read, This technique was ultimately thrown away, due to the fact that most of the soldiers were getting injured for the sake of "Warmth". (Can you blame a guy who's been through Hell? I'd probably do it too, if I went a few years without seeing a single female around [Clothed or Otherwise] )
That being said, a more logical response from Naito would be, "Aren't YOU supposed to be the one warming ME?"
Reading Anime has taught me a great many things. If I'm not mistaken, Most of what happened in Berserk took place during the time of The Crusades. So somewhere between 1095 and 1272. My Brother RedDSlayeris a bigger Berserk fan than I am. He's into Action-y stuff like Berserk and Basilisk, while I like the Pervy Action stuff like High School of the Dead and The Melancholy of Haruhi Suzumiya.
LIKE IT?!?! Lets just say I'd slay a million Hollows to take Naito's place.......Actually, I take that back...Hazuki is my favorite (Sorry. Saya, but she stole your spot).