Please be serious. This comparison is laughable, the ≈ $300M listed on his foundation is literally 0.7% of his net worth.
(Throughout history in many cultures, people gain status by ostentatious gifts of wealth. Of course, that means you have to tell everyone of your benevolence. And as everyone knows, Koch uses his wealth — and shows like this — to wield enormous influence in politics.)
Not that hard. Social justice advocates increasingly view support of free speech as equivalent to defense of racism/sexism/homophobia/etc.
Also, the idea of having Facebook at the cost of giving up your privacy to this behemoth, and more importantly, at the cost of this company exploiting your cognitive biases to get you to buy things hardly seems conducive to a spirit of bettering the world.
http://www.kochfamilyfoundations.org/foundationsdhk.asp
Also rest assured that Facebook also "evades taxes" in the same way that the Koch brothers do, that is by taking advantage of the US Tax Code in a legal way. And none of us have any idea what the Koch Brothers have in their wills and have not publicly announced.