That is just a tactic used by the pro-Israel lobby to undermine and discredit anyone who questions the actions of the Israeli state - you are dismissed as beign an antio-semite, even if your views and valid and you are clearly not being anti-semitic. They will not allow anyone to de-couple the Israeli state from the Israeli/Jewish people.
No-one wants to be slurred as an anti-semite, as you can't defend against such allegations and it wouold serioously hamper any author, documentary maker etc in the US. so as a tactic it works to suppress open debate and questioning of Israel in the US. Ironically it does more to suppress free speech than any notion that such books might be banned would be likely to do.
It is a debating tactic - not about free speech. It's no different than the English Labour party in the 1990's discrediting its own members who supported the principle of Free Education by labelling them all 'Trots', to steer people who feared the left of the party away from supporting the principle and towards supporting Tuition Fees