Being inactive makes a good person bad! (5)
I believe the answer is:
still
'being inactive' is the definition.
('still' can be a synonym of 'inactive')
'a good person bad' is the wordplay.
'a good person' becomes 'st' (saint).
'bad' becomes 'ill' (associated in meaning).
'st'+'ill'='STILL'
'makes' acts as a link.
(Other definitions for still that I've seen before include "Static photograph" , "Source of alcohol" , "sort of life" , "not bubbly" , "activity of one manufacturing spirits?" .)