If you ask me, it just needs a range limit on it and it'll be balanced. That way they can't sit at a high point and snipe you across the map with a now-non-recoil LMG, without even needing to actually see you.
Treyarch can't even manage to properly make maps or balance guns/perks so I didn't expect them to be able to handle attachments.
I thought the red dot sight was a noob attachment in CoD 4 when it first showed up. Part of balance achieved with weapons was by the use of iron sights (and sway which has been forgotten). Just think of how many players used the irons on the M16 in Cod 4, only people who didn't have the red dot unlocked because the majority can't aim at all.