The law needs to be tightened to prevent the abuse of free speech by those who would praise terrorist actions, the Lord Chancellor has said.
Lord Falconer says a free society must defend itself against terrorism
He said proposed new laws to outlaw the glorification of terrorism would reduce the "fertilised ground" for extremists.
Human rights campaigners fear the plans may result in liberties being lost and those silenced becoming "martyrs".
But Lord Falconer told Radio 4: "A free society has got to properly defend itself against terrorism."
He added: "It has got to preserve free speech as much as it possibly can."
'Line needs drawing'
The government wants new powers to ban organisations which glorify terrorism and to prosecute "extremist" bookshops which sell terrorist propaganda or handbooks.
"The line has got to be drawn in relation to things that might cause acts of terrorism; it's not necessarily a proven link - if the risk is high enough," Lord Falconer told programme The World This Weekend.
He said that current incitement laws were not definite enough in what they covered and that new legislation was needed.
However, playwright David Edgar said it was possible any new laws may also cover the actions of violent stage characters in their scope.
And Labour MP Joan Ruddock also criticised the plans, saying that while "moral condemnation" was understandable, she did not believed criminalising those who glorified terrorists would work.
She said it would create "enormous problems" for the courts and could also create "martyrs" in the eyes of those they were trying to turn away from violence.