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Ok, nevermind. I think I understand. You'd have to negate all the energy if Earth was a point mass, but since you can still hit the earth without hitting the center of gravity, you wouldn't have to negate all of it. Just a good bit of it. But I don't really see how it would provide a velocity advantage over launching it from the Earth or Earth orbit.

Wait. Kepler's third law I think. area swept out along a curve is proportional to velocity. Things go slowest at apogee, and fastest at perigee. So coming from the moon, its a more highly eccentric ellipse than from earth orbit or ground level, meaning it will be going faster at perigee when it hits. Ok, I understand now, but that still doesn't answer the terminal velocity question.