Naively optimistic (6-4)
I believe the answer is:
starry-eyed
'naively optimistic' is the definition.
(starry-eyed can mean idealistic)
This is the entire clue.
(Other definitions for starry-eyed that I've seen before include "Romantically optimistic" , "Naively enthusiastic" , "Out of touch with reality" , "Naively idealistic" , "Full of unsophisticated optimism" .)