Wire-tapping and creating digital profiles on the other hand is something that I can totally see happening since nobody is really getting "hurt" and you can split up the work between different groups of people that really have no idea what they are working on. But I do not see something like that happening to satisfy some end-goal like gaining control of the public. I don't think we humans can organize that well. There are too many groups with their own interests in mind to be able to unite an entity as big as our government (or parts of it) to pull off most of the conspiracies that go around.
Why does everyone say this? You create 'terrorists'; have them hi-jack a plane, and crash it. It really takes what, 50 people MAX, including the terrorists. One Mission Planner, however many terrorists...a few benefactors, some intelligence guru's; and that's pretty much it. Maybe a guy or two planted to interfere with birds going up to shoot down the planes but even that is a bit questionable as to 'needing'.
Everyone wants to say that oh the NYPD would have had to have been involved and the fire department would have known...noooo...they reacted as they normally would.
Not saying I really believe it was an act by my own government...or fine, part of my own government; but I just wanted to point out that not everyone and there mother would have been involved...really just a few guys and gals in the grand scheme of things.
The simplest and most plausible theory is simply that Bush and Cheney knew, but didn't do anything because they needed the attack to go into Iraq. Even then, at least tens of people in the White House and upper echelons of US intelligence would have known and would have known that they could have stopped this by making a few phone calls. Even 12 years later, not one of them has regretted his complicity in killing thousands of civilians and spilled the beans to a reporter.
Because the most popular theories about 9/11 conspiracies are never as simple as you outlined. I think a small group did plan and carry out the attack, and a part of the US government is just as capable of doing that as Al-Qaeda.
But once you start adding extra details (the buildings had explosives, the pentagon got hit by a missile, etc), the number of people you need "in on it" starts to climb. That is why so many people point out the huge headcount of the supposed conspirators.