Firing pins are made of different metal and temper than days of old. Dry firing does not hurt MOST modern CENTERFIRE guns. The exception is alloy framed revolvers without steel firing pin bushings. Dry firing these, without a snap cap, can result in a bulged firing pin hole.To address your point, if you're concerned about dry firing, inserting a snap cap will absorb the energy from the firing pin when you pull the trigger. I agree with others, that dry firing is not harmful to most modern pistols (not sure about revolvers, though).
RIMFIRE guns should not be dryfired due to the possibility of the firing pin striking the cylinder and leaving a divot that will make it hard to extract, and sometimes, impossible to load until the divot is ironed out.