I wouldn't say I have an answer
But simply put.
Do we exist? - Why not?
In this chapter there were alot of refferences to perception altering machines, even a refference to "The Matrix"
Lets use that.
Even if we were hooked up to such a machine.
We still must exist to be able to be hooked up to it.
Our perceptions may be false, but out existance necesarily isn't.
We can't be hooked up to a machine that we're not around to be hooked up to.
Or
Even if we're part of a simulated universe.
Purhaps some amazingly powerful computer simulation created by a very advanced speciese.
We still exist as data in their simulation.
I don't think that we can validate existance through what we percieve, more that we validate our existance because we perceive, however wrong those perceptions may be.
Regardless of wether we're being influenced by a perception altering machine, or part of a simulation, we still exist as part of them.
From my point of view even though we might not be able to prove we do exist, we'll never be able to prove we don't. Comprehending that I, or we, or anything doesn't exist, or how things would be if all that didn't, isn't something we, or at least I can't grasp.
If we truly didn't exist, and there was nothing to make us exist, none of this would be happening, though thats a meaningless argument because we wouldn't know, because we wouldn't have anything to know, or anything to "know" with. But now I'm rambling...