Only Roman Catholics make it out to be dirty.
Some Catholic writers may have been out of bounds in there understanding of sex, nonetheless Catholics don't view sex as dirty:
2362 "The acts in marriage by which the intimate and chaste union of the spouses takes place are noble and honorable; the truly human performance of these acts fosters the self-giving they signify and enriches the spouses in joy and gratitude."145 Sexuality is a source of joy and pleasure:
Sourc: CCC
Except for Mary after the birth of Jesus.
The implication is sex is dirty, otherwise Mariology comes crashing down.