No aspect of US foreign policy down the years could justify "the events of last Tuesday", the Tβnaiste, Ms Harney, told the House.
"Make no mistake about it: the blame lies fairly and squarely with the people who hijacked the four aircraft and with those who funded and directed them. The blame does not lie with the United States and it is wrong to suggest that it does."
This was important, said Ms Harney, because it was "now being suggested" that a change in US policy might somehow "placate the fundamentalists" and stave off future attacks.
"It is doubtful if anything less than the outright destruction of Israel and the United States and possibly of the entire Western way of life would satisfy the bin Ladens of this world and their fanatical followers."
Ireland was not neutral in the fight against international terrorism, she said.
"The question of Irish military involvement is unlikely to arise, but we can play our part in other important ways." Ireland could be vigilant in terms of security to ensure that this country was not used as a safe haven or staging post by terrorist elements.
"And we can be understanding of the fact that the American government has a legitimate right to deliver an appropriate military response in the wake of what happened last Tuesday."
Global terrorism required a "global response", Ms Harney said. The US needed to build a broad-based international coalition to prosecute this campaign successfully.
This would be a "variable geometry" coalition with some countries playing larger roles than others.
The coalition would not hold, however, if military action by the US and its major allies resulted in large-scale civilian casualties.
"This is a struggle which the US cannot afford to lose. It is a struggle, which the Western democracies cannot afford to lose. I have no doubt that the organisers of last Tuesday's atrocities have the resources and the evil enterprise to repeat them, either in America or in Europe. That is a threat with which civilised people cannot be expected to live."
Terrorism had disfigured the politics of this country for much of the last 30 years, the Tβnaiste said.
"Proportionate to its population the island of Ireland has had its Manhattans and its Pentagons. We remember Enniskillen and Omagh, Greysteel and Loughinisland and 100 other places whose names are written in blood in our history." As the whole world turned against terrorism it was time for Ireland to escape from its history - time to put the past behind us.
"There are still several organisation on this island which seek to engage in political activity while still keeping the terrorist option open. Some are actively engaged in violence, others are on ceasefire."
It took courage to move away from violence, more courage than it took to kill people, said Ms Harney. "I would say this to all of them: the doorway to democracy is now open. Go through it. Take your courage in your hands. Say, now, in clear and simple terms that you are renouncing the use of violence for political ends and that you are prepared to take your chances with the rest of us in the democratic process." That meant no more guns, bombs or punishment beatings, Ms Harney said. "Don't just say it, do it."