Bad Media and optical lens(es)

Hey all i have read that certain media, particularly low quality media can cause damage to optical drives and the lens. ie on a PS2 it has been said that you run the risk of damaging the lens when using poor quality dvd/cd media. Whether this is true or not i was wondering how exactly does the quality of the media effect the lens? On a total and flat out assumption the lens doesnt physically touch the media does it? or does rereading and scanning of poor surfaces cause wear and tear to the lens? this forum section seemed like the best place for this question. Thanks!

i thought it would have to make the laser work harder

i.e. wear and tear.