Let me just put down my 2 cents point of view.
IMHO, you don't need vulgarities to train an efficient army,
neither do you need to curse and swear to get the point
across.
I am speaking from experience, because I do not use all kinds of
vulgarities on soldiers, and all have turned out fine. It may
achieve even better results than you may be thinking now.
This is from a commander's point of view. (After the recruit has
finished BMT and has been posted into a unit). As for whther
bulgarities are needed during BMT itself before the recruit become
a private, that is for your debate.
Nonetheless, I think to swear at recruits during BMT is not
necessary too. You can get the point across in other ways, if you
command the respect of the men. And from my experience, if you
curse and swear at recruits, you will probably gain no respect from
them, only.. dislike (to say the least). And that is not something
you want.