I, for one, am for dual spec as well. I do respec multiple times a week (sometimes a day) for various reasons. I tank for my guild when we run hardmode flashpoints and ops. I don't play a tank because I enjoy it, I play it because if I don't, we don't run anything and I would rather play a role I don't enjoy and be doing content than the other way around.
So when I pvp, I play assault and respec shield if needed for my friends.