Reasons:
-in the heat of battle it can sometimes be confusing whether you have the launcher active or not
-the way your character holds his gun looks silly when the std launcher is attached (m203 on some guns as well)
-from an immersion/realism standpoint it makes sense: less weight due to not having to carry two primary guns
I know this might come off as nit picky but it would be cool if it was added eventually!
I can actually agree to this. Many times I have been caught off guard by aiming through my scope, pulling that trigger to take down an enemy in stealth ... only to lob a grenade and, as my team loves to say, "stir up the hornets nest". And of course now someone will say "pay attention to your retacle", but honestly in every other shooter game I have ever played, an attached grenade launcher was ALWAYS mapped to a separate key.
So the Op suggestion works, but as an alternate, I'd love it if we could map the GL to a separate key and not our primary weapon key. Keeps it mounted on our primary weapon but lessons the blunders of using the wrong thing when engaging an objective.