For some reason, this breaks in the second visit to Hell's Kitchen (04_NYC_Street). After talking to Paul in his apartment, the barricade to the NSF headquarters is not removed.
Tourism for Deus Ex
A downloadable mod
This mod makes the player undetectable, which means enemies will never attack and you can explore the world freely.
NOTE: This mod is experimental and not fully tested - use at your own risk, though any danger to your install is quite low. Let me know if you run into progression-blocking problems with this!
Copy the Tourism.u file to your DeusEx\System\ folder and run in-game by typing this at the console:
This will load the game's first level with the mod active, and any savegames will retain the mod so you should only have to do this once.