The regime libertarians, who crave “acceptability,” are always attacking those who don’t sellout. Similar to how they attack as being racist, pro-slavery, etc., people who, say, think Lincoln’s war was unconstitutional and immoral. Zinn was not perfect or libertarian, but he was great in many was. See e.g. my posts on zinn The Declaration and Conscription, favorably quoting Zinn, and my post Re ‘Untold Truths About the American Revolution’; Gary Chartier’s post where he rightfully says he is “disturbed by the reactions of some libertarians to the work of Howard Zinn”; and various posts on Zinn by uber-libertarian Lew Rockwell.