The point of having your own race is that it is the responsibility of the car behind to make a safe pass regardless of the class, and the point of sticking to your line is to make sure the faster car can predict what you are going to do and make that safe pass. What Rocky tried to do there was not a safe move, it was a last moment dive to the inside which always carries the risk of the car in front not realizing your intentions. Especially in the dark. And this is exactly what happened.
"Hold your line" does not mean "take the normal racing line". "Hold your line" does mean exactly that. Hold it. Do not change it. Moving your line, moving from one side of the track to the other, is unpredictable. It's the difference between I'm going to continue doing what I'm doing, and I'm going to decide to do something different a some point in the near future. One is predictable based on available data, one is not.
If a driver is going to change his line in order to take his normal racing line, he better be damn well sure he's not going to impede anyone. Yes, it's up to the passing driver to make a safe attempt, but it's also the responsibility of the driver being passed to not turn in on him or directly impede him.
When you start to involve greater and greater speed differences, it becomes ever more burdensome on the driver being passed to not hit anyone, especially when you consider that the commitment distance increases drastically with increased closing speeds. I was in a test day last month with a Pontiac GTP car. The thing was top-flight formula car fast and there I was in my little Miata, thankfully with a humongous mirror. I could check my mirror just before braking for turn 11 at Infineon, see nothing (in other words, no traffic all the way to the apex of 10), and have that Pontiac whiz by on the inside of turn 12. The closing speeds by that point were probably on the order of about 80 MPH, which is huge by any measure, but especially when you've got 40 feet of track to work with, walls directly on either side and an apex to make. It got to the point where if I could even see the car behind me I just gave up the corner, otherwise he'd be riding my bumper by the time I went to turn-in. He had to decide whether to pass me basically then, hundreds of feet back, because the closing speed was so great. And know what? We had absolutely no problems. If I had committed to my racing line in each and every corner where he caught me, I'm sure it would have been much more dicey and dangerous. Infineon is dangerous enough.
Basically what I'm trying to say is if both cars aren't heads up, you'll have problems in multi-class racing. And the Ferrari driver involved in the Rockenfeller incident had blinders on. He made a change in his line too late for Rockenfeller to react to safely and Rocky crashed.