See, now you’ve just identified a market for an awesome (profitable) new product… BATTLESQUEEGEE!
OK, fine, I just wanted to say “Battlesqueegee”.
Many modern machine gun turrets are operated by remote control from inside the vehicle; obviously better protection than any face armor.
You’re missing the most important point. Our soldiers are the good guys. Face shields are only suitable for evil henchmen. 
Agreeing with previous posts about visibility (especially for infantrymen) and weight (latest US helmet designs reduced weight of the kevlar helmet by half a pound).
Also bear in mind that for most of the 20th century (say, 1915-1995), any helmet design was going to be expected to work with a gas mask, which was already pushing visibility/weight to the limit.
The last time I checked, they still work pretty well with a gas mask, but yeah, the presence of the mask would limit the usefulness of an integrated facemask on the helmet.
It’s difficult to shoot accurately with a gas mask, and its eye ports are huge. (ETA: So, as it is already, masks in general really restrict vision thus accuracy thus effectiveness, and that’s without having to tackle the remove-faceplate-attach-gasmask-quickly-or-die puzzle)
I commented on this earlier, but wanted to add: Also: Coverage isn’t as important nowadays because you’ll still die from IED concussion anyways.
Yes, that’s why it’s important to bring an extra hanky with you. 
I thought the words “former” and “Marine” weren’t to be conjoined in a sentence together…EVER!
Former Marine Infantry, current Marine something else?
With the reintroduction of steel helmets in WWI there were attempts to add face protection to the helmets. Such as these, the Germans also had a visor for their helmets but I can’t find a link.
The need for gasmasks and the severe vision restrictions meant that such attempts were virtually worthless. And of course no matter how much steel you hang in front of your nose a rifle or machine gun round to the face will put you down.
Really sounds like folk “etymology” (whatever the word is for the origon of practices rather than words), since military salutes have been around in one form or another since the decidedly unvisored Romans.
No, my understanding from the Marines I know is that you’re just always a Marine, even after your military service is over. For life. Its a death cult thing. They seem to enjoy it…let them have their fun!
That’s “ex-Marine”.
Uh, sure.
“Former Marine” is a perfectly acceptable term to describe someone who has been honorably discharged. For more information, see the Wikipedia.
And they aren’t “infantry.” They are Marines.
True, Army has Infantry. Marines have Riflemen, and the Air Force has those poor dopes who didn’t score high enough on the ASVAB.
That one on the right is particularly amazing, being very nearly identical in form to the classic visored helmet of the late Medieval and Renaissance period armour. It has the pointed face guard (originally designed that way to deflect sword blows.) Yes, something like that would not stop a bullet at all, but it could provide protection against shrapnel.
Spider-Man never has a problem with his eye shields being fogged by his mask.
Not the concept of the salute, but the *form *it takes in most militaries, i.e. right hand raised to right temple. Some indeed say it dates back to knights lifting their face guards to show their face for identification, or to convey the message “I’m going to show you I trust you’re going to be all peaceable like and not hit me in the face by making it easy for you to do so”.
As you intuited, of course, it’s bullshit.
The real story is that underlings at one time had to remove their hats in the presence of a superior officer. Over time, it became allowed to merely touch the brim/visor of the hat to show that they would have removed it were it not bloody awkward to have to do so every 5 seconds (or dangerous, in the case of helmets on the battlefield). As traditions are wont to do, the salute only became more codified once its original purpose was completely forgotten.
But the modern soldier often has an ongoing requirement to shove their face into things urgently. Typical examples might be binoculars, a weapon sight, an image intensifier, a big bulky screenshade thingy round a computer display of some kind, a gas mask, a nice protective patch of ground, etc. etc.
When they’re not shoving their faces into things, generally they’re not being shot at and would appreciate keeping things off their faces, apart from maybe things like sunglasses, sand visors, etc.
Hence the usual option is to kit soldiers out with a swing arm on the helmet, which can have stuff clipped to the end of it (from what I’ve seen usually NVGs or a plastic goggle-type mask) which can be swung up and out of the way. Like this. I suppose there’s no reason why you couldn’t have a nice ballistic mask on the arm, but honestly it seems a bit pointless.
If you’re being blown up, there’s no time to swing down a face guard. If you suspect you’re about to be blown up there are better things to do about it than put on a visor. EOD techs are an obvious exception, but they already have nice chunky shields available if they want them.
If you’re being shot at, you probably want to shoot back (probably harder to aim a rifle with a full-face mask on) or get out of the line of fire (run like hell or else ‘dig a hole with your eyelids’) again probably easier without a mask.