Choose to get involved, having zero alternative (6)
I believe the answer is:
option
'alternative' is the definition.
(synonyms)
'choose to get involved having zero' is the wordplay.
'choose' becomes 'opt' (I've seen this before).
'to get' is a charade indicator (letters next to each other).
'involved' becomes 'in' (to be involved in something is to be 'in' it).
'having' is an insertion indicator.
'zero' becomes 'o'.
'in' placed around 'o' is 'ion'.
'opt'+'ion'='OPTION'
(Other definitions for option that I've seen before include "Right to choose" , "An act of choosing" , "Possible choice" , "Freedom to choose" , "Altenative choice" .)