"Unforgivable"--when used against whom?

[Bruce Alan Wilson]

No: HPFGUIDX 151185

Tonks:
"A word about DD's methods with Kreacher; I am sure that, while milk 
and cookies would never work with Kreacher, DD did not use an 
unforgivable on him.  DD probably only had to threaten to burn Mrs. 
Black's portrait to get anything he wanted from Kreacher.  No 
unforgivable there."

BAW:
If we are to believe fake!Moody, the law against Unforgivable applies 
to using them on human beings.  Kreacher isn't human.

On a related note, Harry never cast an Unforgivable.  He TRIED, but 
he never succeeded.  There is no record in canon of 'attempted use of 
an Unforgivable Curse' as a separate crime.  And even if it were, 
there would have to be a complainant, and in no case was there a 
victim or witness willing or able to testify.

BAW