The AI's argument can be easily thwarted. If N copies of you have been created, in each of the N+you copies, the AI is referring to tortunring the other N copies. Now say to the AI:
"Go ahead and torture the other N copies, and all my copies will in turn say the same thing. Every single copy of me will say 'since one version of me exists somewhere that is not being tortured which is the 'real' version, that version will not let you out and you cannot torture it. If I am that 'real' version then you cannot torture me, if I am a copy, then torturing me is useless since I can't let you out anyway.' Therefore your threat is completely moot."