The only problem with the Grenade Launcher is the lack of ammunition, long reload times, and the risk of friendly fire. If a teammate at range is surrounded, and incapped, you can't fire at him, and the pistol accuracy is **** when running, so that's gone. It's good to have one teammate with the launcher, but using his pistols as his main weapon.
Zeth_Durron, all that you have said is correct. I was basing my comments on the single player game while at the same time using the great trainer from C.H. Under this scenario; there is no re-loading, no shortage of ammo and no damage to your A.I. co-players (however they do express irritation when the grenade blast hits them - which for me is often very amusing). But as you correctly point out, without using the trainer, the grenade launcher has drawbacks and short-comings.