The cam does pull the distributor gear down toward the
oil pump, but the thrust load created by the interaction with the cam is not enough to cause the damage done to the gear I saw from Steve's car. What had to cause that was the distributor shaft having signifigant axial load stress grinding the distributor gear against the landing inside the block, or otherwise clearances itself. Unfortunately for Steve, it appears that the heat generated between the bottom of the distributor gear and the gear landing surface within the block was enough to at least momentarily seize the gear and shred teeth off of the softer distributor gear. The only way this can happen is if the distributor drive gear was installed too "low" on the distributor drive shaft. Don't make the mistake of assuming that just because it comes from MSD that way, that it's correct.
YMMV
BK