It's a bit more than that. Zinn's book universally concentrates on the bad things in our history, so that anyone reading it would be convinced that America is worse than Nazi Germany. This is not surprising since Zinn is an unabashed communist, but it is disturbing how many people agree with him.
Here's an article from Newsweek on what conservatives dislike about the College Board's new AP history course.
http://www.newsweek.com/whats-driving-conservatives-mad-about-new-history-course-264592
If you feel that the important points about America in World War II are Japanese internment, infringement of civil liberties, and debate about whether we should have dropped the bomb, you will love the new curriculum. If you think that rather misses the point, you will not.
It's also worth pointing out that these are mostly the same people that brought us Common Core, so if you think that's a good idea you'll likely approve of this too.