Why might it be bad? Why might it be good?
There are so many factors. For one, I'd rather have someone in government who understands technology. So many parts of government are lacking in basic technical capability.
On the other hand, I find Facebook's awareness of the social fabric to be somewhere between inchoate (that's charitable) and a convenient illusion that is fundamentally mostly marketing-driven. (I don't fault a company for being market-driven; however, such incentives are not structured to properly serve people and communities).
But I don't know too much about Facebook's social design as compared to Zuck's goals for possibly serving in government or where he would like Facebook to go.