I don't believe that humans can be "blank slates" in the truest sense of the term. We all have instincts and drives which arise from our biology that come hard-wired into our composition. A "blank slate" would seem to imply a kind of innocence or mindlessness or "pre-programmed" state of being.
I feel that the title question is an incomplete set of options. It might be better to re-state it as:
Are human beings inherently evil?
Are human beings inherently good?
Are human beings born as "blank slates"
Of course this requires some agreement upon the definitions of "good", "evil" and "tabula rasa"...
Perhaps substitute "selfless" for "good" and "selfish" for evil. Either way it would seem that human beings are somewhere on a spectrum between those options. I personally feel that we lean towards the "selfish".
damn. You're awesome