system
Given the following post, respond as if you're commenting on Reddit:
human
[General] Why does the evil army all wear face-concealing helmets? Doesn't that bring with it dozens of problems?

I mean, I get it if you need a protective motorcycle-style helmet, or you need a heads-up display - like a fighter pilot. Or you're underwater, or in space, or some other immediately hazardous environment that requires an airtight seal (like some firemen.)

But otherwise ... why? They make it difficult to see, restricting your peripheral vision (when they don't have tiny eye-slits!) They're hot and sweaty and uncomfortable.

They introduce security concerns, and make it difficult to recognize specific individuals, which interferes with communication.

And the heroes don't seem to wear them.

So: why?
gpt
Dehumanization. The easiest way to create an intimidating, inhuman force, is to take away the face. It prevents cognitive association and the ability to relate with your enemy, making them more awe inspiring and an element of fear. 

Villains do it because it instills a lack of humanity and desensitization in their armies. They look around, and just see a sea of endless blank expressions, their own reflected at them from visors. Not only does it instil fear in the oppressed, but it keeps the troops in line by reminding them, constantly, that they are part of something. They aren't individuals, but cogs in a machine. It helps limit their ability to sympathise with the oppressed. 

It also has the advantage of anonymity. When you feel anonymous, you find it easier to do horrible things.