In my mind, I'm picturing this being used to shoot pretty much blocks of solid materials, not anything delicate, so the only issue is how much they are slowed down; by the time we could build something like this, fabricating in space is not going to be an issue.
Of course, by the time we could build this (assuming its even possible), mining asteroids could already have surpassed it.
Of course, by the time we could build this (assuming its even possible), mining asteroids could already have surpassed it.