Why is it seen as crazy to believe 9/11 was an inside job?

When someone tells a story and it doesn't stand up to reason, or science, you say 'okay, you're lying. What's your motive?'

Yet if you say that about 9/11 you're a crackpot.

Isn't taking someones word without proof crazy? Maybe not crazy, but the epitome of naivety?

Take this for example.
QUESTION: Can we see the footage of the plane hitting the pentagon?
ANSWER: No. But trust us, there was a plane.
QUESTION: Why can't I see it?
ANSWER: National security. It's classified. Don't ask again. Here, a frame of the fireball. Go play now.

Doesn't this sound like a terrible abuse of power? Shouldn't you be suspicious of someone who won't back up their claims with evidence that we know exists?

QUESTION: You know all of the hijackers who were at several airports that day. Can we please see footage of all of the hijackers? Maybe boarding the planes?
ANSWER: No, you may not. That's classified.
QUESTION: But it will prove that they were at least at the airports that day.
ANSWER: Just trust us. They were there.
QUESTION: But...
ANSWER: CLASSIFED!

Why is it because its "the government" that people go "oh okay, that's fine."?

So now my point of view is that its crazy to actually believe anything the government tells you if they aren't backing it up.