Sweet writer is thoughtless (9)
I believe the answer is:
foolhardy
'thoughtless' is the definition.
(thesaurus)
'sweet writer' is the wordplay.
'sweet' becomes 'fool' (type of dessert or sweet).
'writer' becomes 'hardy' (Thomas Hardy).
'fool'+'hardy'='FOOLHARDY'
'is' acts as a link.
(Other definitions for foolhardy that I've seen before include "daredevil" , "Rash - incautious" , "Dry loofah for quality of rashness" , "Reckless" , "Impulsive" .)