Do kickstands damage the frame by being used? I was told once that kickstands warp the frame when used, especially when the bike is laden down, and that some materials are more susceptible to this than others. Is there any truth to it?

I have 36 years of experience using kick stands on cro-moly (steel) and aluminum frame commuter bikes and several years working in a bicycle shop in which time I have never seen any such "warping". Its the kick stand itself that may be in jeopardy when the bike is "laden down"; there are center balance kickstands for tandem and other heavy/awkward bikes. The more likely damage you will get from a kickstand is from over-tightening where it is attached to the frame.