I have many books by liberals. They are not all 100% false. What they can be is completely misleading even if they are a 100% factual.
If someone sites Zinn, I can read his own words, and I can certainly tell if Zinn is being quoted or paraphrased. I can tell if someone unknowingly was influenced by Zinn. I can read Zinn's work and then on any subject Zinn wrote about, I can and did get a dozen or more books that let me figure out what is true, what is the true context. What is the big picture.
I would be ignorant if I only read books that confirmed by opinions and beliefs. I would also not be very effective in a discussion.
Addressing what Zinn wrote about Indians, led me to discovering the greatest books on Indian history, authorized by congress, wrote by schoolcraft, in the 1800's. Very difficult books to find, under $500 each. There are 7 of them, I have 6. If I find one for around 50 I will finish that collection. I have a copy of Bury My Heart At Wounded Knee, and a bunch of other great books about indians.
Zinn opened to my eyes, to his hate, to Zinn's marxism. I learned that Zinn taught Communism to communists, although there is no proof Zinn was a member, there is proof that Zinn was surrounded by communist friends.
Zinn is everywhere, anyone who states the USA was evil for doing such and such, even if they dont know it, it came from Zinn.