My first reaction to the idea is why exactly would they need to be missiles with their own propulsion and other guidance system launched at destinations?
We're already launching thousands upon thousands of tons of minerals at a time from mass drivers from one planet to another and having them arrive safely at the destination. So if a civilisation was so inclined why wouldn't they simply develop more sturdy shipping coffins that hold 1 person with enough internal systems just to keep the occupant alive. And then the planetary mass drivers could launch thousands of colonists at a time at the destination.
At the end of the day, solving the 'surviving launching people in space coffins from mass drivers' engineering problem would probably be more efficient and practical then developing a consumable one-use intelligent human missile system approach.
Well without another mass driver to catch them, mass driver packets are orbital bombardment...
Hmmm an option to just launch packets of rock from mass drivers, use them for Actual Moon is a Harsh Mistress style bombardment...