Attacking cherished beliefs (12)
I believe the answer is:
iconoclastic
'attacking cherished beliefs' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for iconoclastic that I've seen before include "Criticising cherished beliefs" , "Attacking cherished beliefs or institutions" , "Nonconformist" , "Image-breaking" , "Anti-establishment" .)