Conspiracies are just that. Conspiracies. They are made up by groups with an agenda and who gloss over the facts to arrive at the conclusion they were already prepared to accept, rather than adjust their theory in light of new evidence. I've seen numerous conspiracies debunked by simple photographs, so I remain skeptical of many without enough circumstantial evidence that their theory is not only plausible, but actually likely to be the case.
Why do I say this? Because while you may be right that there was a conspiracy to allow foreign agents onto US soil with the intention of kicking off the 911 plot, until I see actual, plausible existence, then it goes into my specially labelled bin called 'horseshit', which happens to include a nice cross-cut shreader and also handles part of my identity protection.
You are correct that deliberate negligence is to blame. The CIA's powers are not limited to operations beyond US soil, nor are all the FBI's powers. These are agencies that are tasked with protecting US interests both domestic and foreign via investigation and surveillance. However, since they must justify their annual budgets, they must prove they are worthy of those budgets, and so they tend to be very secretive in regards to sharing information with other agencies. This means that when one side has the piece, they're not likely to tell the others, "I got this piece what do you have?". It paints an incomplete picture. And honestly? Most terrorist cells are going to be operating alone, in secret, making intelligence gathering difficult. So yes, negligence and a mental attitude of "This is mine, go away" has only hurt the intelligence community.
The Empire of Japan killed 2,400 military personnel and 57 civilians at Pearl Harbor.
In response we burned down pretty much every major and medium sized city in Japan, and made a good start on the lower level cities and A-bombed them not once, but twice.
We ended up killing 323,495 Japanese Civilians and dehousing millions more from their homes.
So no, the USG does not turn the cheek.
You're assuming the Japanese considered everyone on the mainland civilians when they were actually considered part of the army, even if a last-ditch army made up by sheer numbers. They had people in their yards sharpening sticks and swords in an attempt to prepare for the invasion. Large factories were built in the center of residential areas to make it easier for civilians to get there and build more weapons of war. The military was prepared to fight until the entire Japanese people were completely destroyed rather than accept the dishonor of surrender, and had taught entire generations of people that this was the way of things. That this was a fight to the bitter end to defend their homes against the barbaric invaders.
Yes, firebombing the cities was bad. Yes, bombing civilians in general is bad. But when the enemy will not stop, will never stop, you have to finally say, "Do whatever it takes."
Casualty estimates were based on the experience of the preceding campaigns, drawing different lessons:
In a letter sent to Gen. Curtis LeMay from Gen. Lauris Norstad, when LeMay assumed command of the B-29 force on Guam, Norstad told LeMay that if an invasion took place, it would cost the US "half a million" dead.
In a study done by the Joint Chiefs of Staff in April, the figures of 7.45 casualties/1,000 man-days and 1.78 fatalities/1,000 man-days were developed. This implied that a 90-day Olympic campaign would cost 456,000 casualties, including 109,000 dead or missing. If Coronet took another 90 days, the combined cost would be 1,200,000 casualties, with 267,000 fatalities.
A study done by Adm. Nimitz's staff in May estimated 49,000 U.S casualties in the first 30 days, including 5,000 at sea. A study done by General MacArthur's staff in June estimated 23,000 US casualties in the first 30 days and 125,000 after 120 days. When these figures were questioned by General Marshall, MacArthur submitted a revised estimate of 105,000, in part by deducting wounded men able to return to duty.
In a conference with President Truman on June 18, Marshall, taking the Battle of Luzon as the best model for Olympic, thought the Americans would suffer 31,000 casualties in the first 30 days (and ultimately 20% of Japanese casualties, which implied a total of 70,000 casualties). Adm. Leahy, more impressed by the Battle of Okinawa, thought the American forces would suffer a 35% casualty rate (implying an ultimate toll of 268,000). Admiral King thought that casualties in the first 30 days would fall between Luzon and Okinawa, i.e., between 31,000 and 41,000. Of these estimates, only Nimitz's included losses of the forces at sea, though kamikazes had inflicted 1.78 fatalities per kamikaze pilot in the Battle of Okinawa, and troop transports off Kyūshū would have been much more exposed.
A study done for Secretary of War Henry Stimson's staff by William Shockley estimated that conquering Japan would cost 1.7-4 million American casualties, including 400,000-800,000 fatalities, and five to ten million Japanese fatalities. The key assumption was large-scale participation by civilians in the defense of Japan.
Considering they had 500,000 purple hearts manufactured just for one campaign, and this is only for US casualties, I think in the end dropping atomic weapons was the better choice.
Now, I'm going to go out on a limb here and put forward that you're wondering why we went all the way. You can thank Germany for this one. After WWI, the German people were angry and bitter after being made to disarm and surrender, facing huge fines for the war, etc. It was decided that since we'd been attacked by the Japanese and we'd declared war against Germany that we would not stop until we were in direct control of both countries. The reason for doing so is obvious. You take their heartland, force them to submit, and then you rebuild them. You do this and you teach the next generation that yes, yes we could have left you in bombed out craters, but instead we're going to help you rebuild your infrastructure and farms and everything else. What comes out at the other end is a country that may harbor a bit of resentment, but they also know that you've rebuilt them from the ground up.