A report for Europe's human rights watchdog has called for greater scrutiny of secret services and support for whistleblowers.
The Council of Europe investigated how countries like Britain, Germany, Romania and Lithuania assisted the US with the rendition of terror suspects.
It said a "cult of secrecy" had helped Western governments cover up abuses.
Defending "whistleblowers", it singled out US soldier Bradley Manning, accused of passing secrets to Wikileaks.
He had "acted as a whistleblower and should be treated as such", CoE rapporteur Dick Marty wrote in the report, which was due to be submitted to the CoE's Parliamentary Assembly.
The soldier is currently in a US military prison awaiting trial for passing restricted material to the controversial website.
But the report praised Mr Manning, and Wikileaks itself, for uncovering evidence of rendition.
The CoE represents 47 member-states, including both EU countries and Russia and other ex-Soviet states.
Mr Marty's report focused on the record of Western states, explaining that it was based on investigations into European links to the controversial US policy of "rendition" for terrorism suspects.
The CIA allegedly flew terror suspects around the world for interrogation in the years after 9/11, holding them in secret prisons in Europe and elsewhere.
'No licence to kill'
In his 48-page report - entitled Abuse of State Secrecy and National Security - Mr Marty looked at the level of control exercised by European states over their security services.
He urged all states to use independent parliamentary committees to oversee the work of their secret services, saying this was of "vital importance for the rule of law and democracy".
Mr Marty argued that Western governments were using the notion of state secrecy to shield their intelligence services from accountability for serious violations committed during anti-terrorist operations.
"We consider that this is simply unacceptable..." he wrote.
"A 'licence to kill' (or to abduct and torture) only exists in certain films, and in dictatorial regimes. In democratic systems, parliaments, as representatives of the people, have a right and duty to know what the government is doing in the name of the people."
Mr Marty praised investigative journalists and non-governmental organisations for their work in exposing abuses of authority.
Stressing the "fundamental role" whistleblowers had to play in an open society, he warned against "a real cult of secrecy... as an instrument of power".
While it was up to the courts to decide if Bradley Manning had committed any crime, he wrote, the CoE was "indebted to him" for the publication of a recording of a helicopter attack in Iraq "in which the crew seems to have intentionally targeted and killed civilians".
Thanks to Mr Manning, he said, a large number of embassy reports had "allowed us to learn significant details of important recent events... which are obviously of general interest".
"We therefore join Amnesty International in expressing our worries as to the treatment he receives," Mr Marty wrote in the draft report.