Sensor fusion allows you to resolve that ambiguity, I wonder if Elon is really as in touch with this as you would expect. No single sensor is perfect, they all have their problematic areas and a good sensor fusion scheme allows you to have your sensors reinforce each other in such a way that each operates as close as possible to their area of strength.
No single sensor can ever give you that kind of resilience. Sure, it is easy in that you never have ambiguity, but that means that when you're wrong there is also nothing to catch you to indicate something might be up.
This goes for any system where you have such a limited set of inputs that you never reach quorum the basic idea is to have enough sensors that you always have quorum, and to treat the absence of quorum as a very high priority failure.
Even if it doesn't allow you to resolve the ambiguity, knowing that there is an ambiguity is extremely valuable. Say the lidar detects a pedestrian but the camera doesn't. Which one do you believe? Well, you propagate the ambiguity and take appropriate action, i.e. slow down, change lanes, etc. Don't drive through an area where there's a decent chance that you're going to kill someone by doing it.
Yes, absolutely. Knowledge about the fact that a conflict between sensors exists is valuable in its own right, it means you are seeing something that needs more work than simple reinforcement.
Fail safe, always. That's what I tried to get at with 'absence of quorum', it means you are in uncharted territory.
Last time I checked I relied entirely on vision to drive autonomously.
That's a very naive way of looking at this.
You have an extremely detailed world model including a mental model of the drivers and other road users around you. You rely on sight, sound, experience and lots of knowledge. You are aware of the social contracts at work when dealing with shared resources and your brain is many orders of magnitude more powerful than any box full of electronics.
What you can do with 'just vision' misses the fact that you are part of the hardware.
You also have hearing, you can move your head and wear sunglasses to avoid glare, etc.
You have a much better GPU than it has.