Welcome, Futilitarian. Your question sets a poser but I will try to formulate a response.
To fix ideas, I assume that torture is (1) the deliberate infliction of physical pain or psychological suffering (2) beyond a threshhold of mere mistreatment (c) applied by a state actor in order (d) to gain information (e) relevant to the vital security of the state (or community) where (f) it is known for certain that the person tortured possesses the required information.
This will not cover all cases of torture - of course not - but it will give us a starting point.
1.It is possible to hold that torture is always morally wrong and should never occur. Let's consider the weaker position that torture is always morally bad. Moral judgements are sensitive to considerations of pain and suffering (among much else) and so it follows that the use of torture (as defined) is always morally bad, always a moral evil, always something that has moral disvalue. But badness does not entail wrongness. This is clear from the many cases in which we have to act and our action has to be a choice of evils. We choose the lesser evil, X rather than Y.
This means that both X and Y are bad. It seems clear to me that, so far as pain and suffering go, i.e. employing only that moral criterion, the equal pain and suffering of 1000 people (X) embodies greater moral disvalue than the torture of 1 person (Y). It is in your language 'a worse act'. This rests on a comparative judgement of the numbers of persons and their equal experience: it is morally worse that more rather than fewer people should equally experience deliberately applied pain and suffering.
Here in the words of your question group sufffering is worse than individual suffering.
2.To turn now to the second possibility: if torture is morally bad, for the reasons just given, is it always morally wrong? If you hold the principle that torture is always morally wrong and should never occur, that practically ends the discussion. Are there, however, or could there be cases in which the torture of 1000 persons does not embody as much moral disvalue as the torture of one person?
I need to change the terms of the example. Suppose the one person is innnocent and does not have the information his torturers require. Suppose also that the 1000 do have this information. If the torturers of the one person are persecuting him because as a dissident he fails to vote for the ruling pary, then his torture is morally wrong as well as morally bad.
If the information-possessing 1000 will not disclose what they know, conditions are imaginable in which for the sake of the survival of a community of millions, torture at the minimum level necessary to extract the information would be justified in terms of communal self-defence. If (as is widely acknowledged) it is morally justifiable, and in that sense morally right, for me to kill in self-defence, is there not a parallel with a state's right to torture in self-defence? Here is a case where the torture of 1000 embodies less moral disvalue than the torture of one.
Here in the words of your question individual suffering is worse than group suffering.
Two caveats: (1) such conditions, while imaginable and not wholly unrealistic, are so rare that they would (even if my parallel works) hardly ever justify torture and make it morally right. (2) The means of torture remain subject to moral constraints.
If torture involves merciless beatings, powerful and dangerous electric shocks, 'rape, acts which resemble drowning and suffocation, burning with fire and chemicals, sensory deprivation, the witness of the torture of others, especially loved ones, and threats of the same, and sham execution' (Blakely: 376) then these are not justified merely because, and if, torture is justified. Extreme discomfort, yes and with compunction and regret, but not acts such as these.
I am less than certain about the above arguments. But they represent what I am currently inclined to think. If they contain errors, these can and I'm sure will be easily exposed.
Ruth Blakely, 'Why Torture?', Review of International Studies , Jul., 2007, Vol. 33, No. 3 (Jul., 2007), pp. 373-394.
Ben Juratowitch, 'Torture Is Always Wrong', Public Affairs Quarterly, Apr., 2008, Vol. 22, No. 2 (Apr., 2008), pp. 81-90.