Knowledge should be free.
I generally agree with this, but people choosing to profit is not evil at this point in our evolution, and may never be.
seven of the largest companies on the planet, whose sole business plans are to exploit the free exchange of information by putting up artificial barriers and charging for access to things
This is true as far as their own IP goes, but this isn't generally true even for Apple and Microsoft. Google in particular is doing quite the opposite. They are providing access to all the information they can, for the cheapest possible price. I don't really see how any other large companies are doing this either.
They're creating the next Dark Age
You can't even accuse Microsoft of that. You might have argued they've slowed things down a bit, but "Dark Age" is pretty fucking far from reality.
the power imbalance between the information-rich and the information-poor is growing, exponentially.
There's some truthiness here, if you squint a bit...however the "information-poor" is rapidly heading towards zero. So what's really happening is that everyone is becoming enriched.