I agree. The oil is not
I agree. The oil is not damaged. It never is. It is only contaminated.
He is correct on the heat cycles, however. Short drives back to back (anything less than 15 minutes) allow three things to happen. First, the engine does not heat up to operating temperture, allowing the oil to be able to do its job of cleaning the engine of internal deposits. This gums up the engine over the long haul. Second, it does not allow the engine to heat up and evaporate off the gasoline that leaks into the oil past the piston rings, diluting the oil. Third, on short runs, gasoline does not burn completely, and the oil accumulates carbon particles from poorly burned gasoline and from the extra gasoline that is added to the cylinders to accomodate the engine being cold.