I think sex within marriage carries as much or little as weight as the couple decide it should.  But if, God forbid, my penis were cut off, there would be no less love in my marriage, nor would my marriage be in jeopardy.  I think because of modern perspectives in sex (thanks to Kinsey the quack, et al.), too many people over-emphasize the importance of sex in life.  The Catholic Church has understood that sex, while undeniably a strong drive, can be controlled (hence the expected chastity of priests) and does no have to play an important role, or any role except for reproduction, in marriage.  Indeed, many people live happily in sexless marriages, particularly those who have matured beyond their sexual peaks.

Ironically, the sexual liberation movement that arose simultaneously with the feminist movement has been a windfall for men, making their lustful demands for sex almost a requirement for women to comply with.  My college-age daughter told me sex is a prerequisite to dating!