The ARD does other jobs too. Believe it or not it keeps fingers, gloves, garbage from touching the lens. Not a problem now but wait until a lookie lu picks up your rifle. Also it keeps brush, rocks (yes rocks,.. you are a soldier and not standing all the time) other crap from building up when you dont want it too.
The ARD is a good device for the field. Trust me. Been there, done that. If you realy hate it and feel it needs to be off your M68. Unscrew the sucker when you deploy or hit the range. It comes right off. Put it back on when you turn your weapon back in.
BTW some field advice. Put some 100 MPH tape on your lens covers. I saw hundreds of M68's during OIF without any lens protection. They will get yanked off over time without tape unless your not not a field type.