According to these reports from the BBC and "Democratic Underground", whom both I have decided to trust about this, the Israeli secret service had tried to warn the US about the 9/11 terror attacks in advance and to prevent them.

The American intelligence agency, the CIA, could have prevented the 11 September attacks if it were not for systematic failures, according to the German newspaper Die Zeit.

The paper has uncovered details of a major Israeli spy ring involving some a 120 agents for the intelligence service Mossad operating across America and some masquerading as arts students.

The ring was reportedly hard on the heels of at least four members of the hijack gang, including its leader Mohammed Atta.

But the Israeli agents were detected by their American counterparts and thrown out of the country, it says.

...

Just a month before the deadly attacks, the paper said, Mossad handed over to the Americans a detailed report naming several suspects they believe were preparing an attack on the United States.

http://news.bbc.co.uk/2/hi/europe/2294487.stm


Remember this:Mossad warned CIA of attacks 9/11

Mossad officials traveled to Washington last month to warn the CIA and the FBI that a cell of up to 200 terrorists was planning a major operation, according to a report in the Sunday Telegraph here yesterday.

The paper said the Israeli officials specifically warned their counterparts in Washington that "large-scale terrorist attacks on highly visible targets on the American mainland were imminent." They offered no specific information about targets, but they did link the plot to Afghanistan-based terrorist Osama bin Laden, and they told the Americans there were "strong grounds" for suspecting Iraqi involvement.

A US administration official told the paper that it was "quite credible" that the CIA did not heed the Mossad warning: "It has a history of being over-cautious about Israeli information." But the official noted that "if this is true, then the refusal to take it seriously will mean heads will roll."

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=125x9847

According to iags.org (whoever they are), the total cost of the 9/11 attack (for the US alone) was this:

Counting the value of lives lost as well as property damage and lost production of goods and services, losses already exceed $100 billion. Including the loss in stock market wealth -- the market's own estimate arising from expectations of lower corporate profits and higher discount rates for economic volatility -- the price tag approaches $2 trillion.

Among the big-ticket items:

The loss of four civilian aircraft valued at $385 million.

The destruction of major buildings in the World Trade Center with a replacement cost of from $3 billion to $4.5 billion.

Damage to a portion of the Pentagon: up to $1 billion.

Cleanup costs: $1.3 billion.

Property and infrastructure damage: $10 billion to $13 billion.

Federal emergency funds (heightened airport security, sky marshals, government takeover of airport security, retrofitting aircraft with anti-terrorist devices, cost of operations in Afghanistan): $40 billion.

Direct job losses amounted to 83,000, with $17 billion in lost wages.

The amount of damaged or unrecoverable property hit $21.8 billion.

Losses to the city of New York (lost jobs, lost taxes, damage to infrastructure, cleaning): $95 billion.

Losses to the insurance industry: $40 billion.

Loss of air traffic revenue: $10 billion.

Fall of global markets: incalculable.

http://www.iags.org/costof911.html

According to Representative Ron Paul, who doesn't know that Egypt and Israel are not enemies, the bill for Israel's services to the US is about three billion dollars (with two billion dollars going to Egypt).

http://www.lewrockwell.com/paul/paul363.html

(And no, I do not agree with Ron Paul that "many Israelis" regard all those Muslim states that get foreign aid from the US as "enemies". I happen to know that the vast majority of Israelis really doesn't care whether Indonesia gets money from the US. Generally Israelis support US aid to Egypt and Jordan (and now Iraq) and other stable Arab countries.)

I assume that the US usually don't throw out Israeli agents in pursuit of terrorists that plan to attack US infrastructure and citizens. Based on that assumption it appears to depend on the terrorists' stamina whether terror attacks of that scale are planned often and we don't know how many have been stopped by the CIA when not in full failure mode. (And no, the terrorists do not attack "great satan" because of his support for "little satan". And neither do the terrorists kill Muslims in Iraq, Afghanistan and Pakistan because of either the US or Israel.)

Three billion dollars a year (which are mostly spent on American arms) are not a high price for preventing another Holocaust (and its associated costs) and getting at least some protection from common enemies. (Plus it means that American weapons are constantly being tested for their ability to scare other states from attacking.)

Either way, one must help one's friends.

And your friends are those who try to protect and help you, not those who tell you how you brought a catastrophe onto yourself because of your immoral lifestyle.

Of course, here is what really happened: http://xkcd.com/690/