I've had college professors who were like Foner. Some were exceptionally interesting lecturers, while being actual communists. One in particular stood out. He's dead now, but I was stunned when he defended Stalin in class once. It's a shame that intelligent people fall for the leftist line. But leftists need something to believe in also, and radical socialism is their religion.
You bring up several important point in your post. Many Americans labor under the illusion that somehow, in a university education, there exists the beginning of wisdom. This is a fallacy. Wisdom comes from the inherent values the student brings to the table. And they better have said values before they get to college or the enlightenment of their education will have little more effect than a Cambodian Re-Education Camp.
Foner, for all his brilliance, honestly believed America was the most evil empire in human history and Republican administrations were no better than Hitler and the Nazi regime. This is nothing new for leftist thinkers (and you're right about the distinction between leftists and liberals).
The very fact that such people are so deluded is proof positive that the university in the 21st century is a breeding ground for treason the likes of which we have not seen this side of your garden variety Soviet Politburo. If the war on terrorism accomplishes nothing else, hopefully it will clean out this nest of traitors once and for all.