I don't know a whole lot about mass drivers, but from what I've seen, I don't think they're workable on Earth for the reasons you've pointed out. I think there was even a proposal for one that was supposed to use a massive magnetic levitation system to keep the whole thing pointed at the sky, which just seems far to ridiculous to work in real life.
I think mass drivers will be constructed on the moon once there's an established human presence there.