The problem seems to be that you guys have been taught only one side of the story. Benjamin Franklin proposed two theories. The first was called the lightning dissipation theory and the other the lightning diversion theory.
Lightning dissipation theory argue that the primary role of a lightning rod is to discharge the cloud over a longer length of time, thus preventing the excessive charge buildup that is characteristic of a lightning strike.
The lightning diversion theory states that a lighting rod protects a building by providing a conductive pathway of the charge to the Earth.
Lightning researchers are now generally convinced that the lightning dissipation theory provides an inaccurate model of how lightning rods work. It is indeed true that the tip of a lightning rod is capable of ionizing the surrounding air and making it more conductive. However, this effect only extends for a few meters above the tip of the lightning rod. A few meters of enhanced conductivity above the tip of the rod is not capable of discharging a large cloud that stretches over several kilometers of distance.
NOTE: As Benjamin Franklin suggested the lightning rod doesn't need to be sharp and now it's shown that blunt tips work much better.
The virtue of sharp tips for strike reception has never been established. An examination of the relevant physics shows that very strong electric fields are required above the tips of rods in order that they function as strike receptors but that the gradients of the field strength over sharp-tipped rods are so great that, at distances of a few millimeters, the local fields are often too weak for the development of upward-going streamers. In field tests, rods with rounded tips have been found to be better strike receptors than were nearby sharp-tipped rods.
Hope this explains it.
