There is a passage in "Conversations with Yogananda" where Swamiji mentioned Master having said that "Women lead a two fold life where they drink man’s blood in the night..." and have always wondered since about what Master meant? With all the love and gratitude I feel for him in my heart, I still can’t fathom what what he must have meant. Surely with Master, it can’t be sexism, or was it just a seemingly harsh analogy used to instill discipline in the monks he was speaking to?
—Nirja , India
You are right: Yoganandaji was not sexist. And certainly women do not drink men’s blood, nor by any means are all women temptresses. As you surmised, he was using stern language to help his monk disciples remain celibate. (He might have made a corresponding remark about men to his nun disciples, but being a male, Swami Kriyananda would not have been present to record such words.)
Men, especially younger men (as many of the monks were), can be prone to sexual preoccupation, even if they do not pursue sex outwardly. This is both a waste of time and a spiritual impediment, for it directs one’s life-force outward to the senses, strengthening their hold on the mind, rather than inward and upward, where it could have aided spiritual growth. The guru’s strong admonition was intended to help those monks avoid such preoccupation. He was metaphorically emphasizing something that he said elsewhere: in orgasm men lose a large quantity of life-force, and it can take a good deal of time to replenish that energy.
That’s why the great masters teach that, unless the purpose of sexual union is procreation, that energy that would be better spent in seeking God.