The new level cap and quests/dungeons/instances' rewards will quickly make t0/t0.5 obsolete anyway (remember, t0 starts at level 52/53) xD So no point doing that silly Baron 45 run.


Anyway, back to the BE. Their main motivation is not evilness (regardless of the quote of the BM in TFT, since Metzen has the "Bend Lore" talent, and used it), but rather desperation. This is all the more true that the BE in TBC are not joined with Kael'thas (they seek a way to reach the Outlands and Kael'thas), and meanwhile are trying to deal with their addiction. Also, when/if you'll play the low level BE quests, you'll see there's a fairly clear distinction between the BE junkies and the BE in the Horde.