The Intelligence HQ is the most dangerous site in the game right now, by my understanding, so I'm not sure there's any good way to make it much harder, just more complicated.
Agreed.
I actually disagree with the Intelligence HQ as host site being the hardest option for two reasons. First, Agents don't wear body armor of any sort, so if you can get a bullet past their admittedly high dodge rating, they go down like flies, unlike Hardened Veterans or SEALs (who typically lay there for a round or two drawing fire away from their able fellows, leading to more casualties). Second, the player can head to the Intelligence HQ on day one (if they start with a car), whereas simply finding CCS hideouts is a whole adventure in itself. Hence, my arguments for "part two" of the CCS List being in the first CCS hideout.
Aside from the two points Darvi & Neonivek made (either of which suffice to break the argument, IMO), the most one would have going for an action on the Intelligence HQ on Day 1 would be
an AK a Bug,
3 points of Rifle 7 points of Martial Arts, 3 points Security, 2 points Stealth, and 2 points Computers. No armor & no disguise; probably not enough Stealth or Security to accomplish anything, and no chance at the Supercomputer (needs 8 Computers, minimum, IIRC).
I would be very interested to see someone do a Day 1 site action on the IntHQ, gain Juice (ideally, make it to Activist or level up a skill), and come back intact. Hitting the Supercomputer within the first month might be theoretically possible but would be a grindfest. One would be looking for 9-10 in Stealth/Disguise, Security, and Computers. That last one would probably be the killer, since the most one can start with is 4, if I'm reading the questions wiki-page correctly. (By comparison, the car is trivial.)
<puts on JFK mask>
"I believe that this Squad should commit itself to the goal, before January 2009 is out, of
Liberally Hacking the
CIA Supercomputer and returning all involved safely to their safehouse."
<removes mask>