Tom, if having an upper limit on disutility(Specks) that's lower than disutility(Torture*1) is begging the question in favour of SPECKS then why isn't *not* having such an upper limit begging the question in favour of TORTURE?

It should be obvious why. The constraint in the first one is neither argued for nor agreed on and by itself entails the conclusion being argued for. There's no such element in the second.