Ray Boisvert said Thursday the Canadian Security Intelligence Service had the resources to monitor only those threats "in the red, high-risk, high-probability zone" when he served as the agency's assistant director of intelligence earlier this decade.
"That meant that we had no time to even consider looking at any sort of lesser evils that were emerging out there," Boisvert told the House of Commons public safety committee, which is studying a sweeping new security bill.
Boisvert, now a security consultant, said he takes "great offence" to commonly voiced concerns that the legislation would effectively place legitimate protest under the CSIS lens, adding that groups and individuals "should not flatter yourself to that degree."
Boisvert and David Harris, another retired CSIS officer, backed a legislative proposal to allow the spy agency to actively derail terror plots — not just gather information about them.
It would give CSIS flexible options to handle threats, Harris told the MPs. "These can be very important in moving decisively when there may be a risk situation developing," said Harris, also a private consultant.
Under the bill, CSIS could take clandestine measures that violate the Charter of Rights and Freedoms as long as a judge approves the actions.
CSIS was established in 1984 during the thick of the Cold War, when the operational tempo was much different, Boisvert said.
"Quite often, an intelligence officer would arrive from the Soviet Union. We would take four years to decide whether or not that person was truly an intelligence officer. In today's threat environment, sometimes you have weeks, sometimes days, sometimes hours."
The disruption provisions would conscript judges into the "dirty business" of spying, said Ziyaad Mia of the Canadian Muslim Lawyers Association.
"It turns the role of the judiciary completely upside down," he told the committee. "This is not the role of judges in our system."
The Conservatives brought in the 62-page security bill following the murders of two Canadian soldiers just days apart last October. There was no direct link between the attacks in Ottawa and St-Jean-sur-Richelieu, Que., but it appears both assailants were inspired by radical Islamic thinking.
The bill would also make it easier for police to limit the movements of a suspect, expand no-fly list powers, take aim at terrorist propaganda on the Internet and dismantle federal barriers to sharing security-related information.
The NDP opposes the legislation. The Liberals plan to support it, but outlined several proposed changes Thursday, including creation of a full-fledged national security committee of parliamentarians.
Boisvert acknowledged there was "deep concern" about the legislation and endorsed the notion of augmenting the existing watchdog functions of the Security Intelligence Review Committee.
"We were a better organization because of review, not despite," Boisvert said. "We knew everything we did would eventually at some point face some form of review by somebody."
David Cape, chairman of the Centre for Israel and Jewish Affairs, praised the bill's terrorist propaganda provisions as well as the move to outlaw the act of encouraging someone to commit an attack.
But he also called for stronger scrutiny of CSIS activities and recommended the intelligence review committee chairman be made an officer of Parliament. He also called for more efforts on deradicalization of extremists and tighter privacy restrictions on the bill's information-sharing measures.
Zarqa Nawaz, creator of television's "Little Mosque on the Prairie," said an informed citizenry is the best defence against extremism.
During personal reflections about her life as a Muslim in Canada, she expressed concern about the recent wave of disrespectful comments about Islam.
"This isn't who we are as Canadians."
Follow @JimBronskill on Twitter
Also on HuffPost