Asmodeus: No, you're not obligated to use the scope to aim the M203, but you can. If you go back up to near the top of this page, where I said, "I would like to see the Inf team make that change, so that when you properly aim the M203 on an M-16/ACOG/M203 combo while looking through the scope, all you see is blue sky (not the target the 40mm will strike). Since aiming the M203 through the scope is very easy and effective right now, and it's impossible IRL, it's unfair/unrealistic and should be changed.
Try this: M16 with M203 only (no acog) and aim the M203. The iron sights and barrel obscures the spot where the 40mm grenade will strike. Obviously, if you add an acog to that combo, you would not be able to see the target through the acog (the barrel would still obscure the same spot, and what you will see through the acog will be something well above the target). Yet, in the current Inf M16/M203/acog loadout, you -can- see where the 40mm will strike, and with the assistance of the acog you can place the grenade very accurately. Now, the only explanation for this, if it can be accomplished in real life, is that the M203 mount is different when the acog is added, with some elevation of the M203 barrel, to the point that the M16 can be lowered, in turn allowing the target to come into view. Maybe that's how it's done, I don't know.
The bottom line is this: DO real life soldiers use the acog scope to aim the M203 (which carries a distinct advantage to placing the 40mm grenade), or not? It's really that simple. If they do, then things are fine the way they are. If they do not or cannot, then Inf soldiers should not be able to, either. What I don't understand is why there's even any disagreement about this.