I agree that dagger+shield trolls are annoying, but it's not like there is any realism argument against using a dagger with a shield. They are more easily countered than an agility shielder with a regular sword, due to the shorter reach and crappy sideswing damage; just backpedal and kick, or nudge and let your teammates one-hit them.
The only problem with daggers in general is that it doesn't seem like the animation can keep up with the weapon speed; you get hit by the stab before the animation indicates you should. However, the counter is just to hold downblock and don't attack until you hear the block; same as fighting a roflcopter pikeman.
