To argue falsely is a scandal (7)
I believe the answer is:
outrage
'is a scandal' is the definition.
(I've seen this before)
'to argue falsely' is the wordplay.
'falsely' indicates anagramming the letters.
'to'+'argue'='toargue'
'toargue' with letters rearranged gives 'OUTRAGE'.
(Other definitions for outrage that I've seen before include "Offend - atrocity" , "Scandal" , "scandalous!" , "Gross affront to decency" , "Gross injury" .)