Daggers use their own animations.. and Daggers can only be dual wielded and used well by Rogues. Combat is the odd man out not the other way around and you can still use daggers for combat pve and not many combat pvp anyway.
Daggers have no mechanical difference from Swords, Maces, Axes, etc, save a tendency to faster speeds and slightly different animations. The only reason for this distinction is flavor, and that flavor is reason we're the only class who requires four sets of weapons for one role (PVP, PVE; Combat and Dagger for each)
Dagger combat comes at a massive performance penalty and is about as valid as an Enhancement shaman wielding a dagger, or a Druid using a fist weapon and only that.
There is no excuse for trivial flavor to affect gameplay.
The rogue class as a whole would benefit if daggers were normalized a la fist weapons (all set to a 2.6 speed, tuned appropriately, and all weapons for all specs). Furthermore, they would become a viable option for Enhancement shaman, who have had fairly legitimate itemization complaints through the last expansion or so and would enable Daggers to be useful to a class that isn't Rogue.
Rogues are a class of archaic ideals. Weapon and positional requirements are a handicap with no benefit and should go the way of the old weapon specialization talents.