I'd imagine in public he'd declare it pointless but shrug it off, while in private seeing it as an atrocity.
I am not so sure I'd expect Garak to classify it as an atrocity. He was a cruel man himself, who believed getting his results was worth any price (he even tortured Odo and who knows how many other people, or committed murder(s)), so I wouldn't assume that anyone's suffering made any impression on him. Especially if that suffering was non-Cardassian for the good of Cardassia.
In a Cardassian library
or in a Cardassian gallery
"Reagan, it appears, is really only an ardent unionist if the unions in question are in Poland" - Stephen King, Skeleton Crew