Elsewhere in the world, the issues are not so black and white. An internet poll of 470 New Zealanders on Telecom's Xtra site gave a narrow 53 to 47 per cent vote against instant US retaliation, while the BBC website shows dissenting voices from around the world.
"An attack on Afghanistan would be totally immoral," says Londoner Jo Clayton. "Military action does not discriminate between those who support a regime and those forced to live under it."
One possible solution - which has struggled for traction since President George W. Bush first uttered the magic words "war against terrorism" - is to find Osama bin Laden and put him on trial.
Michele Malvesti, a former terrorism analyst with the US Defence Department, says this would be difficult and could only be used alongside military, diplomatic and economic measures, not as an alternative.
Malvesti, who is now a doctoral student at Tufts University in Massachusetts, has some experience in the area. She advised on the US response to the bin Laden-directed 1998 embassy bombings in Kenya and Tanzania, which resulted in 302 guilty counts for four of his followers in a Manhattan court in May.
She says that if America and the world are serious about a genuine, long-term war against terrorism, legal action might prove more effective than broad military strikes, which usually fail to achieve their objectives and would further alienate the Arab world.
But it would probably take a huge political shift to convince the US public to treat the September 11 attacks on the World Trade Center and Pentagon as a crime punishable by law.
So were the attacks really a criminal act or were they - as Bush says - an act of war?
Technically, they were both, says Malvesti.
A presidential directive defines terrorism as both a crime and a national security threat, effectively allowing the Administration to choose how it responds.
Hardliners regularly argue for military action; others like herself lean towards legal action, backed by covert operations, as a more effective long-term response to terrorism. She admits there are problems, starting with the obvious difficulty of finding the chief suspect.
Could the US catch bin Laden?
Many analysts believe this is what American and British special forces are trying to do in Afghanistan already - although their primary mission is probably to kill bin Laden rather than bring him back alive.
Few expect there is much chance of capturing the al Qaeda leader in the near future. His security arrangements will be tighter than ever and it would be difficult, if not impossible, for special forces to catch him and bring him out of Afghanistan to face trial.
Capturing bin Laden would therefore be a long-term option, requiring much greater US cooperation with other intelligence agencies.
The service that could help most is Pakistan's Inter Services Intelligence (ISI), which has close links with the Taleban. The problem is that many ISI agents remain sympathetic to bin Laden - despite their President's controversial decision to side with America - and are deeply suspicious about sharing information with the CIA.
If bin Laden was brought to justice, where would he be tried?
The Taleban initially suggested that it might give up bin Laden for trial in an Islamic country, an idea instantly dismissed by the US.
Leaving aside the threat of political interference and the lack of openness in many Islamic courts, it would not be credible in the eyes of America or the world.
Malvesti expects the US would probably demand a trial in a federal court, since the crimes happened on American soil. There have also been rumours that the White House is considering some kind of military tribunal, where the accused would have fewer constitutional rights than in an ordinary court.
The answer could eventually depend on the circumstances of bin Laden's arrest. If the US caught him, it could ignore a likely outcry, particularly from some Arab nations, about his chances of a fair trial in America.
But if there is a realistic prospect of a third party handing him over, some diplomatic horsetrading over the venue seems likely, even though Bush has repeatedly said there can be no negotiation over American demands.
Could the trial be held in a neutral country?
The logical compromise would be the new International Criminal Court in The Hague, in the Netherlands.
Its jurisdiction will cover crimes against humanity, including murder committed as "part of a widespread or systematic attack directed against any civilian population ... in furtherance of a state or organisational policy to commit such attack."
Unfortunately, the court does not have retrospective jurisdiction, so it cannot deal with crimes committed before its statute - agreed to in Rome in 1998 - comes into force.
That will not happen until 60 countries have ratified the statute. So far, only 37 have done so, and the US is not among them. It has been a reluctant supporter of the court, fearing that its own citizens might be brought before it.
Even when the court starts investigating and prosecuting those suspected of war crimes, possibly by 2004, it would be powerless to act against individuals who are protected by states that have not ratified the treaty.
Anywhere else then?
Politicians could use the Lockerbie formula. The trial of Libyans Abdel Basset al-Megrahi and Al-Amin Khalifa Fahima, accused of bombing Pan Am Flight 103 over the Scottish town of Lockerbie in 1988, eventually started last year under Scottish law but on neutral territory at Camp Zeist in the Netherlands.
After almost nine months it finished in January, with the three judges finding Megrahi guilty but Fahima not guilty.
Many diplomats regarded it as a triumph that the two were brought to justice at all, but, as Malvesti concedes, the not guilty verdict on Fahima was greeted far more cynically in defence and intelligence circles, particularly in the US.
"Many hardliners in the intelligence community didn't feel that justice was altogether served."
Could the US prove bin Laden carried out the attacks?
On Monday, Secretary of State Colin Powell insisted that it could. He promised to release a dossier of evidence that would convince Arab nations which were calling for proof of bin Laden's complicity before they joined any US coalition which targeted him.
Yesterday, however, Powell changed his tune and said most of the information was classified.
Malvesti says a legal prosecution team would have the same dilemma about compromising intelligence sources and methods - only worse as courts demand a higher standard of proof than the political arena.
There is strong circumstantial evidence. Allowing for false identities, about 11 of the 19 hijackers were Saudis, like bin Laden, and several had fought in Afghanistan or in other conflicts which he supports.
German agents reportedly bugged a known bin Laden cell which celebrated wildly at news of the attack, with one voice exclaiming: "We did it, we did it!"
And the FBI's best lead so far could be the arrest last week of Boston taxi driver Nabil Almarabh, believed to be one of bin Laden's top agents in the US.
What would the defence say?
It would probably emphasise the lack of any direct connection with bin Laden. The main difficulty in making charges stick is that bin Laden allegedly finances the terrorist networks in al Qaeda but leaves it to leaders further down the chain to decide on the attacks themselves.
One CIA source told the Observer newspaper that it was even possible bin Laden did not know about the September 11 attacks until after they happened.
Rival intelligence agencies, such as Israel's Mossad, have suggested that other terrorists could have planned the attack.
So far the claims have not been taken seriously by the US, but they would be picked up by any defence lawyer who was worth his fee.
There seem to be a lot of snags. Wouldn't it be simpler just to bomb Afghanistan?
It would be at first, but a military strike could lead to even greater problems.
The advantage is a clear, visible response, which meets the American public's demand for retaliation. The disadvantages are that bin Laden and his organisation would probably escape, many innocent Afghans could die, the Arab world would turn against the US, and bin Laden - who dreams of a Muslim holy war against America - could become stronger.
Writing in the Boston Globe after the guilty verdicts in the 1998 embassy bombings, Malvesti argued that the legal approach had been more successful than America's counter-terrorist military strikes against Libya in 1986, Iraq in 1993 and bin Laden himself in 1998.
Yesterday, she acknowledged that there was a groundswell of support for strong action now but said the US could not afford to have public opinion polls dictate policy.
"I think any type of overt military strike might help us in the short term in selling US resilience in the face of these attacks. But ultimately in the long term they will not prove effective in dismantling terrorism, nor in bringing the perpetrators to justice."
Map: Opposing forces in the war against terror
Afghanistan facts and links
Full coverage: Terror in America
