I really hate when people say "Sorry for the hate" and just go on and hate anyway.
Yeah, Zinn was a real leftist socialist lunatic. He brought the struggle of many different indigenous people in the colonial era to light. He made us see that there was a price paid for success. The winners of history don't just get there by leaving a nice neat trail behind them. So yeah, he really sways history by trying to be proactive in taking another approach to history and trying to see what else we can learn from it.
Zinn should be respected on the basis alone that he brought this kind of "loser" view of history to the attention of so many people, for better or for worse. I don't think we can think of many other historians who did something like this.