Would you rather have 1 person suffer and save over 100 people or have over 100 people die and terrorist have life long sentence? Torturing the one terrorist will prevent further terrorist activities by letting us be prepared for them. Thus, increasing safety of the general population. We can get so much information about them and erase their threat over us.
Pro's resolution is that torture should be allowed for usage on terrorists.
As Con, I assert that torture is unreliable and could end up proving to have more negative effects than positive ones.
Burden of proof is shared.
Torture: The act of causing severe physical pain as a form of punishment or as a way to force someone to do or say something. 
Why Torture Doesn't Work
Any information gained from torturing a person is extremely unreliable. There's no way to know if the detained person is giving correct or false information. People who know nothing may try to tell lies to temporarily stop the torture and these lies may end up causing more harm than good. Even when the person being tortured does know something, they may give false information anyways to stop the torture and to not betray their cause. A person under extreme pain from torture will say anything to stop the pain, even if it's temporary. Because of this, torturers rarely can even determine what's true and not true in the information they extract. Because of this unreliability factor, it's pointless to torture someone as you're more likely to get false information that will damage the cause than true information.
The inflicting of severe trauma on a human being can damage short term memory. Ribot's Law essentially states that after an occurrence which included something extremely traumatic, a person will show a temporary variation of retrograde amnesia.  That being said, on top of the argument above, any information produced has a high potential of not being accurate.
Applying This Knowledge
Now that we've discussed the essence of why torture doesn't work, let's apply it to Pro's scenario.
If torture actually worked and they could accurately extract the information from the one terrorist to save the 100 civilians, it would be obvious to conclude that the end justify the means. However, the probability of them extracting true information and not lies or inaccurate information is extremely low given what's been discussed. The chances of the prisoner giving false information that could lead to the harm of others as well as the 100 are too high to take the chance. Torture is simply too unreliable.
To conclude, torture is a inefficient way of gathering intelligence because it is heavily unreliable. Pro must provide evidence/reasoning to support torture and successfully refute my arguments to win.