Ive never had a problem opening or closing a door when a tire is off the ground. The rear gate will catch just a tad, but thats why is has the little wedge that lines it up.
If you think about it, the only thing on the door that would add strength is the hinges, and the latch. The latch isnt really HD enough to add any strength to the Uni-Frame. The rear gate on the other hand has an extra latch that gives it strength.
I have riden in a YJ with the doors off and I must say its kinda cool on the HW. Passing Coal trucks can feel very unsafe though, and a side impact would be bad news for sure... But a side impact in an old YJ would probably be sad anyway.
Youve got to look over those people that talk about the KJ. Most people on here take theirs in some fairly crazy places, which proves anyone out there that says the kj cannot go offroad wrong. Even if they see pics or not.

_________________
LOST KJ'S
Where are you going???
Current Jeep: 2004 Jeep Liberty
-Atlantic Blue
-Air Ride Rear Suspension ; OME/Rustys Lift ; Powertrax Locker ; Moog Lower Ball-Joints ; 245/70/16 Yokohama Geolander A/T-S's on MOABS ; Flowmaster 50 SUV
Lost #007082
http://www.cardomain.com/id/jeepjeepster