It appears that Kimball's sentiment hearkens back to statement made in April 1942 conference by President/Prophet Heber J. Grant, which was also repeated in a First Presidency message to church youth:
“Sexual purity is youth's most precious possession. It is the foundation of all righteousness. Better dead, clean, than alive, unclean.”
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Message of the First Presidency, Heber J. Grant. April 1942 General Conference
So despite all of the later backtracking, we get this sentiment from at least two Mouthpieces Of God On Earth™.
This language was apparently bounced around quite a bit between Q15 members. From an article called
Rape and LDS Teachings: http://squaretwo.org/Sq2ArticleHarrisonRape.html
Marion G. Romney, in the April 1979 general conference, quoting a First Presidency statement of April 1942: “…better dead, clean, than alive, unclean…”[5] Essentially the same words are found in writings by Harold B. Lee,[6] Bruce R. McConkie,[7] Spencer W. Kimball,[8] and in a quote from Sir Walter Scott’s Ivanhoe, noted by President McKay.[9] Further confusion arises from basic misunderstanding of rape. Bruce R. McConkie in Mormon Doctrine, in a section on chastity, confuses rape with voluntary sins such as fornication, homosexuality, and masturbation.[10] In The Miracle of Forgiveness, President Kimball, speaking of a woman’s being raped, says, “If she has not cooperated and contributed to the foul deed, she is of course in a more favorable position.
[5] Marion G. Romney, Ensign, May 1979, pp. 41-42; Conference Report, April 1942, p. 89.
[6] Harold B. Lee, Stand Ye in Holy Places (Deseret Book, Salt Lake City, 1974), pp. 332, 376.
[7] Bruce R. McConkie, Mormon Doctrine (second edition) (Bookcraft, Salt Lake City, 1966), p. 124.
[8] Spencer W. Kimball, The Miracle of Forgiveness (Bookcraft, Salt Lake City, 1969), pp. 63, 66.
[9] Llewelyn R. McKay (compiler), True to the Faith: Sermons and Writings of David O. McKay (Bookcraft, Salt Lake City, 1970), p. 37.
The Salt Lake Tribune printed:
This message was preached repeatedly by LDS leaders of that era and in a widely read church volume, President Spencer W. Kimball’s “The Miracle of Forgiveness.” It was encapsulated in a 1974 LDS First Presidency statement, which asserted that only if a woman resisted an attacker “with all her strength and energy” would she not be “guilty of unchastity.”
I have not seen the exact wording of that 1974 statement but the FP backed off shortly afterward, as the often do when everyone else in the world points out to them how insensitive and uninspired they are, and released a second, softer statement:
It is conceivable that a woman could be so terrified by mere threats of violence or death made by an attacker that her sense of agency would be overpowered, causing her to submit without making a real show of resistance … . Under these circumstances, we feel that the safe course is for leaders of the Church to urge sisters who are threatened with rape to resist to the maximum extent possible or necessary under the circumstances, leaving it to their own conscience and good judgment as to the degree of such resistance. Furthermore, because of lack of knowledge of the circumstances involved, which only the parties to the rape would know, we should not presume to judge a woman who has been raped and who survived, leaving such judgment to the omniscience of the Lord. (136. First Presidency statements, 29 Mar. 1974, 8 Apr. 1974.)
“The easy confidence with which I know another man's religion is folly teaches me to suspect that my own is also.” -Mark Twain
Jesus: "The Kingdom of God is within you." The Buddha: "Be your own light."