Unfairly is precisely the point on which your question turns. If you have interesting points to raise in favor of Al Qaeda, you should absolutely be allowed to raise them, and you should not be fired for so doing. I don't think your arguments will have much merit, but if they're cogent, i'm happy to hear them.
The whole point of his manifesto, and the reason why your post misses it, is that he wasn't fired because of the truth or falsehood of what he said. His arguments weren't evaluated on their merits, and presumed to be the wanderings of a mind ill-suited to the tasks at Google's hands. Nobody even bothered to directly address the question of whether he was right, because they were too invested in how it made them feel. That is the problem.
We should be open-minded about everything. Including child labor, ending universal suffrage, and the virtues of Al Qaeda. We should be able to reject bad ideas on their merits, each and every time, because we understand what and why we believe. We should embrace disagreement, because it makes concrete our own worldview. The fact that the VP of Diversity of at Google simply dismissed the arguments of a widely circulated (and therefore, likely, widely agreed with) memo speaks volumes. And it may be that he's wrong. It may be that his arguments are completely empty of substance, maybe the studies he cites are pseudoscience. But if a decent number of Googler's agree with him, as appears to be the case, then his arguments should be addressed directly, on even ground, on their merits - not shamed into silence. If he's wrong, it should be easy to demonstrate it.