One way to look at it is to turn the question around: is it wrong/offensive to refer to God exclusively as male? As has been noted by other responders, although some people can see "He" and read it as gender neutral*, others associate such male pronouns with distinctly male characteristics. Therefore, using male language solely creates the impression -- even if "only" subconsciously -- that God is male. I suppose True_Blue, thrusting Christianity forward into the 12th century, would be happy with that, but I think that most theologians agree that God is outside gender. Add in the wider sociological implications of a patriarchal theology (like, giving the distinct message that women are inferior) and I'd say it is indeed wrong to perpetrate the false impression that God is exclusively male. Hence, it is ok -- even beneficial -- to refer to God as female.
Now, all that said, what I wonder about is why the Church hasn't pushed for plural pronoun usage, as is now becoming common in secular contexts. Modern English usage typically allows breaking number agreement to use plural nouns as gender-neutral singular (eg "If any employee has a problem with the new dress code, they may bring their concerns to their supervisor..."). Why not use They for God? I suppose that might raise some theological (Trinity) issues, but it seems like a good compromise, plus having the advantage of being consistent with secular usage. Any thoughts on this?
* But since that's in the context of God, that's usually because they've been raised in that mindset. For someone with a different cultural perspective, that's much more difficult.