It's hard to know what to say to someone who says that “all torture is indefensible”. Or, rather, you don't know where to begin.
The same is true for this position as it's put by Julian Baggini:
“The first [strategy] is to insist that the torture is in principle wrong. Even if it would save thousands of lives, there are some moral lines that cannot be crossed.”
All you can ask is: Why is torture wrong... “in principle”?
Could it be that many people adopt this position without advancing arguments to defend it? And, in certain respects, that's understandable.*
Torture Saves Lives
If it's deemed to be an almost factual matter (even if only factual in theory, as it were) that if X is tortured he will tell you where the bomb is and thus many lives will be saved, then torturing that person seems preferable to allowing many innocent people to die. Especially since those deaths can be averted.
This is even more the case if the person being tortured is guilty in some way: say, if he's a terrorist who's already killed many innocent people.
We must now ask a simple question:
Why is wrong to torture this one individual if such a thing will save many lives?
Of course it is sometimes argued that torture is ineffective. (Actually, that's not true – it's sometimes ineffective.) We can also say that the victim of torture may be innocent and so on. However, these possibilities are being discounted here. The issue is about torturing a person who is known to be guilty; or who's known to have knowledge of the bomb's whereabouts.
(In any case, arguing about the efficacy of torture can be seen as a practical position; not necessarily a moral or philosophical one.)
So, again, let's say that he is guilty and that the torture will result in lives being saved. After all, let's remember that some acts of torture have indeed saved lives in cases like this. Torture sometimes works.
However, even if torture works (however that's cashed out), it may still be deemed to be wrong.
That Slippery Slope Again
People who are against torture may say that torture will “inevitably go on” on a wider scale if it were legalised. However, that can happen even if it's proscribed. Indeed that's obviously happened on many occasions. (This discounts the reality of torture being “officially denied”yet practised by various authorities or governments.)
It could even be argued that official torture (as it were) will set limits on when and why torture is acceptable; whereas as if it's deemed unacceptable in all cases, it may encourage various authorities to use it willy-nilly. After all, there's a monumental difference between torturing someone in order to save hundreds of lives and torturing someone to gain state secrets. (Or even torturing a petty criminal in order to get him to tell you what another petty criminal is planning.)
This may lead one to the conclusion that when torture can be shown to save many lives, it should be allowed. Though when it's used for petty or insignificant political reasons, it shouldn't. (Of course arguments will be advanced as to how these distinctions can be quantified.) And, again, if torture is rejected (at least officially) out of hand, then these distinctions become irrelevant because all acts of torture are as bad as each other!
Incidentally, it can never be said that legalised torture will "inevitably lead" to anything specific. It depends. And the total prohibition of torture may lead to more gratuitous torture, not less.
The case of what Julian Baggini calls “moral self-indulgence” is also interesting – especially in the case of torture.
Although Baggini doesn't say this, it also appears to be similar – or the same – as moral grandstanding.
To put that simply: it's not important to the self-indulgent moralist whether or not lives are saved, or even what the arguments are on both sides of the debate. What's important to the moral grandstander is to take a strong or absolute moral stance on the matter. Or, in some cases, what matters is how such a person is seen by others or how he sees himself.
Let's not forget here that moral absolutes have also been the domain of the intolerant and dangerous. And that can just as much apply to those who take an absolute position on torture (or on another “human rights” issue) as it can apply to those who take an absolute position on abortion or blasphemy.
And the bottom line (as stressed by Baggini) is that “the charge of indifference to the lives of those left to die as a result is hard to shake”. In other words, one's moral scruples or absolutes (depending on how you look at it) are going to result in many deaths– at least on the scenarios outlined above.
Political Selectivity on Torture
From a purely political perspective, many Leftists only protest against torture when it's carried out by “capitalist states” (such as the US and UK). They virtually never protest about torture in Iran, Pakistan, Cuba, Venezuela, etc. And, similarly, many Leftists (or at least communists) rarely – if ever - protested against torture when it was carried out by the many communist states which existed in the 20th century.
Similarly, many conservatives or right-wingers only protest against torture when it is carried out by communist or Muslim states. They virtually never protest about torture when carried out by regimes they are ideologically or politically happy with (specifically their own countries).
In other words, one's prior politics is determining which acts of torture - or which regimes - one speaks out against.
To add to the political nature of this debate, it can also be said that once you've established an argument that successfully puts the case for torture (if any argument can ever be entirely successful on this - or on any - subject), then the same argument or defence can – or could - be used by literally anyone.
What I mean by that is once you've argued for your own favoured state (or favoured government or institution) using torture, then states (or governments or institutions) you don't politically favour can use exactly the same argument/s in their own defence when they too use torture.
*)To play the devil's advocate: there are examples of psychological and physical pressure which even some – or many - human rights activists would happily engage in. For example, when you shout in a racist's ear-hole. Or when you deny someone food for 24 hours. Or indeed even when you deny someone a single meal.
All three can be deemed to be torture. Mild - or even very mild – torture, sure ; though still torture.