The biggest problem with torture is not whether or not torture is effective. Prisons sometimes rehabilitate people and sometimes not but the main point of a prison is not rehabilitation.
The problem with legalized torture is that almost anybody can be legally tortured. In general, the victims of torture are not tried in a court of law before being tortured. Soldiers and police and administrators/bureaucrats/lawyers decide who is worthy of torture with very little legal oversight.
There should at least be a requirement ... such as needing a torture warrant from an impartial judge. It should be required that torturers present specific evidence as to why they believe the suspect ought to be tortuted and how torture will be conducted.
Personally, I am against torture. It is unpredictable what will be the results. The results can vary from obtaining critical information to accidentally killing an innocent person. And many people have died because of "torture".
In the case of serial killer Anatoly Onoprienko, the police arrested an innocent person and tortured him to death. 17 days later, they found the real murderer.
Who is worse? the serial killer? or the police who murdered an innocent person?
http://en.wikipedia.org/wiki/Anatoly_Onoprienko
"In March 1996, the Security Service of Ukraine (SBU) and Public Prosecutor's Office specialists detained 26-year-old Yury Mozola as a suspect of several brutal murders. Over the course of three days, six SBU members and one representative of Public Prosecutor's Office tortured (burning, electric shocking and beating) the arrested citizen.[3] Mozola refused to confess to the crimes and died during the torture. Seven responsible for the death were sentenced to prison terms.[4] Seventeen days later, the real murderer, Anatoly Onoprienko, was found after a massive manhunt, seven years after his first murder."