I don't like the idea of trading in Lv.50 Pokémon from the start, esp. since they will obey anyone with five badges, allowing complete and total annihilation of the endgame. However, trading in unhatched babies lets one still put the Pokémon under their ID, and thus they become insider Pokémon even if not found normally in-game. I consider this acceptable for a first run even.
With that said, I do have plans to complete the main Dex in that game before fully branching out into the complete Dex. This is why I someday need a used copy of White for the other DS; to trade legendaries over that are not in B2/W2 (and a lot of them ARE found there).
Oh, and I'm trying to clone my Keldeo, and I will be seeking a cloned Genesect from the current event for my Black without trading the new one back.