i think there is a little truth, not a lot, in these 'conspiracy theories' i thought it was very odd that popular mechanics published a debunking article some years ago - it seemed out of place and the author was connected to various politically interested organizations...
more plausible than conspiracy theories is the very provable: Israel and pro-Israel forces had foreknowledge about the attack and let it happen:
The High-Fivers- by Justin Raimondo Israel and 9/11: New Report Connects the Dots- by Justin Raimondo
but even if that were not true...what the admin, and AIPAC's lobby did
after is more important: ignored the reasons for the attack, lied about them, and used it as an excuse to attack israel's enemy: iraq.
Regarding a north american union -that's not conpiriacy theory - its a pretty out in the open plan - that's why bush is ignoring securing our borders and flooding the country with mexican immigrants - realities on the ground.