As in why the hell does the Assault Rifle not have visible iron sights or any sort of targeting reticle? 
 
Edit: Oh, nevermind. Just found my answer.

Futuristic visors mean iron sights aren't needed. Watch RoboCop for proof.

the Spartan's HUD emits a laser that interacts with a laser emitted from his weapons that allow a targeting reticule to be displayed on the visor.

So why does the BR have a sight?

" So why does the BR have a sight? "

The reticles are all projected from a neural implant in the back of the head, I think. There ARE iron sights/scopes/dovetails/posts/whatever on the majority of human weapons in the Halo universe, but to get them all balanced and easy to use for gameplay reasons, they treat them all the same and don't let the player use ADS. 
 
Something similar to the weapons of the humans in Warhammer 40k, a Space Marine can basically aim down the sights no matter where the gun actually is positioned, as if a camera was relaying the shot directly to his eyes.

It's a videogame. It's not supposed to be realistic. 

it doesnt want to be like most other first person shooters around?

they all got those big helmets on

Interesting.

Linked to the helmet, so no iron sides needed.

" As in why the hell does the Assault Rifle not have visible iron sights or any sort of targeting reticle?  Edit: Oh, nevermind. Just found my answer. "

o only has iron sights on ranged weapons. its how its always been and there is no reason to change it to suit cod fanboys

DUDE there is no iron sights in SPACE!

Space truckers don't use iron sights.

The guns aren't made of iron. Duh.

The real explanation...Bungie is too lazy to implement them and is content with pumping out a crappy FPS that sells like hotcakes.

They used all the iron on earth, there is no iron on other planets.

Halo with Iron sights would suck.  Hippopotamus

Wait so how do the marines who don't have a HUD in their helmet use them?

HUD projections... lasers... blah, blah, blah.
  
Next question: Why is the grass in MW2 made of steel?  Grenades make that "tink tink" sound when one is thrown at you when camping in the grassy knolls.

" The real explanation...Bungie is too lazy to implement them and is content with pumping out a crappy FPS that sells like hotcakes. "

" The real explanation...Bungie is too lazy to implement them and is content with pumping out a crappy FPS that sells like hotcakes. "

" The real explanation...Bungie is too lazy to implement them and is content with pumping out a crappy FPS that sells like hotcakes. "

Master Chief is too good to use iron sights.

A wizard did it.

because it isn't cod.

Tradition.  If a game is released at a time when ironsights nor console FPS's were standard, then it's probably going to stick with the lack of ironsights out of tradition.  If they didn't do it by Halo 3, they're not going to mess with what people expect in Reach.
 
Of course there's no canon explanation because it was a logistical and design decision by Bungie used from the first Halo.@caseylakes said:

" because it isn't cod. "

what the hell would be the point? the guns shoot strait wherever you point them if they added them it would just convolute the controls  
the reason that the BR and sniper have them because they benefit from them

To properly aim an assault rifle, you have to press your cheek against the butt-stock while touching the charging handle with your nose. Doing this with a thick helmet is impossible. It's hard enough to aim an M4 with a gas mask on, let alone Spartan Armor. 
 
plus 1 for ridicules logic!

Honestly I just prefer iron sights to the visor zoom, something just feels right about looking down the barrel of your weapon, regardless of the efficiency in future warfare. 
 
Iron sights is literally the thing that made me get into COD... until BF:BC came out.

to repeat an earlier post, the canonical explanation is simply that the master chief's visor acts as a HUD for the weapon he is holding at the time and automatically zeroes the weapon to his needs and provides a crosshair.

" @Fjordson: He's not saying Halo is crappy because it has no ironsights; he's saying its crappy and has no ironsights. I agree. Well, sorta - Halo is fun if you like Halo - I played and bought every Halo game - but played Modern Warfare, Battlefield Bad Company and Team Fortress in between - and now I can't stand Halo.  "

Every game doesn't need ironsights.

Ironsights are a design choice, not an improvement over crosshairs.  
 
I think so, anyway.

" @Fjordson: Yeah; I mean, games of this calibur - I don't know if they could be "bad games" - they just aren't for some audiences. Like BlazBlue isn't a bad game, but it's not for some people. There are good games out there that aren't for everybody. Halo just isn't for me anymore. "

reading some of these posts leads me to believe that alot of people don't read other peoples posts before they type theirs.

" It's a videogame. It's not supposed to be realistic.  "