I may be wrong, but I think the concern was delicate components protruding from the body are susceptible to damage in urban areas.
Cars already have mirrors and lights etc. LIDAR is in the same family as those.
Mirrors and lights are generally cheaper than a whole LIDAR unit when I get lightly sideswiped.
I figure if the LIDAR is mass produced on every car, it won't be much more than a headlight. (Headlight prices notwithstanding)