He has a burning desire to destroy (8)
I believe the answer is:
arsonist
'he has a burning desire to destroy' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he has a burning desire' is the wordplay.
'he' becomes 'ist' (I can't justify this - if you can you should believe this answer much more).
'has' says to put letters next to each other.
'a burning desire' becomes 'arson' (I've seen this in another clue).
'ist' after 'arson' is 'ARSONIST'.
Can you help me to learn more?
(Other definitions for arsonist that I've seen before include "Incendiary, firebug" , "One firing property" , "A major criminal" , "Pyromaniac" , "One who maliciously burns property" .)