If the drunk man stabbed the cop in the eye with a pen, would you argue that a pen isn't a weapon and therefore the cops had no right to retaliate? Obviously, intent plays a big part in the perceived danger behind any tool wielded as a weapon.
The encounter did not begin with him grabbing the tazer.
The encounter began with Brooks taking a nap in the middle of a drive-through lane. The cops responded by attempting to talk to Brooks and politely ask him to move. Brooks responded by grappling with the cops, stealing their weapon, and running from the cops while shooting at them.
The cops did not start this, and they did not escalate it, they simply responded in the only reasonable manner given the circumstances that Brooks created.
For a man who seemed incensed by people ignoring the facts, you don't seem to hot on keeping them on point. Let me help you.
Brooks responded by grappling with the cops, stealing their weapon, and running from the cops while shooting at them. --> Brooks responded by grappling with the cops, stealing a non-lethal weapon, and running away from the cops with a discharged non-lethal weapon.
See how much difference that makes?
Also, on the ballpoint pen problem. A little critical thinking will show you this is an incredibly spurious comparison. A pen is a tube of metal, makes a great shiv. A spoon can be similarly used, particularly if you grind the narrow bit of the head down on some brickwork first. However, we're not talking about a man with a shiv running at an officer and stabbing him in the face.
We're talking about a man running away, holding a piece of plastic (which, even if you binned it at someone's head at best speed probably wouldn't be fatal) which fires tiny tiny harpoons, which are attached to a one-to-two shot battery. A ballpoint pen is considerably more lethal than a taser, and the aforementioned spoon is like miles beyond it. Hell, it's probably still more lethal than a taser when thrown while running away, but if you're genuinely terrified for your life because you're having sharpened spoons lobbed at you by fleeing alcohol induced narcoleptics, you should probably not be a law enforcement officer.