A more accurate source this misconception may be Susan Brownmiller's book Against Our Will, published in 1975. In this extensive study of rape, Brownmiller reaches the conclusion that rape "is nothing more or less than a conscious process of intimidation by which all men keep all women in a state of fear".
It's easy to see how this could be misinterpreted and oversimplified into "all men are rapists". In fact, this is not the point of Brownmiller's statement at all.
Before the 1970s, rape was percieved, both by psychologists and law enforcement agencies as a crime purely about sex. Rapists were theorized to be men who were driven to rape by being denied sex by frigid, "unfeminine" wives, or who were made into sexual deviants by controlling or abusive mothers. Almost no attention was given to rape from the perspective of the victim, or even to examining the statements made by convicted rapists about why they raped.
In her book, Brownmiller discusses the facts of rape, first fully investigated in 1971 by Menachem Amir. Amir discovered several things that completely shattered previous conceptions of rape. First of all, rather than married men with cold wives, most rapists are young, unmarried men. Most rapists reported no other forms of sexual deviancy, but they did show an extreme penchant for violence. When asked why they raped, these rapists indicated, rather than a desire for sexual intercourse, a desire to humiliate and degrade women. Rape was not "a spontaneous explosion of lust", but rather was "usually planned in advance and elaborately arranged".
Brownmiller also theorized that rape is part of a "subculture of violence", a symptom of the machismo that pervades society. Brownmiller concludes:
"A world without rapists would be a world in which women moved freely without fear of men. That some men rape provides a sufficient threat to keep all women in a constant state of intimidation, forever conscious of the knowledge that the biological tool must be held in awe, for it may turn to weapon with sudden swiftness born of harmful intent."
Brownmiller's intent is not to imply that "all men are rapists", but rather that the existence of rape is enough to make all women fear all men as potential rapists.