Okay, a brief thought on the original question of this thread. I'll let you guys hash out the other stuff, I don't think I have the energy.
Think of the original quote. He sited it as necessity, not propriety. Without getting graphic, think of the act we're talking about itself and how the role of the woman differs from that of the man. There
is a certain amount of submission required, or at least
permission. You essentially can't force a man to do that (in the normal way), but you can force a woman. Therefore, for her to do that willing, she
does have to submit, even if she's in control, if you will. She has to allow that to happen, however it's done. I think that may be what he means by necessity.
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It is with words as with sunbeams, the more they are condensed, the deeper they burn. --Robert Southey (1774-1843)