Personally I like Black*Star's voice in English, although, still I agree with most, his Japanese one is AWESOME too.
I think his voice is meant to be high-pitched and girly to show he's immature and hasn't reached puberty yet. -- It's just ironic that "The Man Who Overcomes God" and "The Greatest Assassin Ever" has a voice that doesn't fit him.
If he did have a really deep voice, well, it wouldn't be very funny, and personally, I think it would be a bit creepy.
I'd like to hear if you guys have any comments on his voice!