Sex between a husband and wife is good, ordained by God.
Only Roman Catholics make it out to be dirty.
Consider the exegesis of these church "fathers" (without attacking their piety):
Jerrome:
The same Apostle in another place commands us to pray always. If we are to pray always, it follows that we [priests] must never be in the bondage of wedlock, for as often as I render my wife her due, I cannot pray...Now a priest must always offer sacrifices for the people: he must therefore always pray. And if he must always pray, he must always be released from the duties of marriage.
The skewed conclusion of Jerome is readily apparent in the light of the fact that marital relations are not the only things that may distract from prayer for a time (which does not mean it cannot/should not be practiced prayerfully like other activities), but eating, driving, etc. also may. Thus to be consistent, Jerome's logic is that a minister (which are never called priests as a distinct class) cannot eat or drink, or engage in any like physical activity.
Yet in further seeking to use Scripture to support his skewed view of marriage, Jerome next invokes Genesis 2 and 7, arguing,
"This too we must observe, at least if we would faithfully follow the Hebrew, that while Scripture on the first, third, fourth, fifth, and sixth days relates that, having finished the works of each, “God saw that it was good,” on the second day it omitted this altogether, leaving us to understand that two is not a good number because it destroys unity, and prefigures the marriage compact. Hence it was that all the animals which Noah took into the ark by pairs were unclean. Odd numbers denote cleanness. (Against Jovinianus, Book 1, Cps. 7,13,16,33; http://www.ccel.org/ccel/schaff/npnf206.vi.vi.I.html)
So much for sending out disciples by pairs, while this renowned Bible scholar (for his day) ignores that it was after the 4th and 6th days that God said His creation was God (Gn. 1:18,19,31) Thus according to Jerome's logic even numbers also denote cleanness.
Similarly, Augustine held a perverse view of marital relations, believing that Heb. 13:4 only means the marriage bed is not defiled if fornication and adultery or relations without the intent to procreate is avoided, and that marital intercourse could not be engaged in without sinful passions, though these were excused for Christians. In On Marriage and Concupiscence (Book I, cp. 27) he states,
Marriage is itself "honourable in all" Hebrews 13:4 the goods which properly appertain to it; but even when it has its "bed undefiled" (not only by fornication and adultery, which are damnable disgraces, but also by any of those excesses of cohabitation such as do not arise from any prevailing desire of children, but from an overbearing lust of pleasure, which are venial sins in man and wife), yet, whenever it comes to the actual process of generation, the very embrace which is lawful and honourable cannot be effected without the ardour of lust, so as to be able to accomplish that which appertains to the use of reason and not of lust....This is the carnal concupiscence, which, while it is no longer accounted sin in the regenerate, yet in no case happens to nature except from sin. — http://www.newadvent.org/fathers/15071.htm
Now, this ardour, whether following or preceding the will, does somehow, by a power of its own, move the members which cannot be moved simply by the will, and in this manner it shows itself not to be the servant of a will which commands it, but rather to be the punishment of a will which disobeys it. It shows, moreover, that it must be excited, not by a free choice, but by a certain seductive stimulus, and that on this very account it produces shame. This is the carnal concupiscence, which, while it is no longer accounted sin in the regenerate, yet in no case happens to nature except from sin. It is the daughter of sin, as it were... http://www.ccel.org/ccel/schaff/npnf105.xvi.v.xxvii.html
Similarly, Tertullian argued that second marriage, having been freed from the first by death,
“will have to be termed no other than a species of fornication,” partly based on the reasoning that such involves desiring to marry a women out of sexual ardor. (An Exhortation to Chastity, Chapter IX.—Second Marriage a Species of Adultery, Marriage Itself Impugned, as Akin to Adultery; http://www.ccel.org/ccel/schaff/anf04.iii.vi.ix.html)
The reasoning here would easily extend to any gratification of the flesh, from eating chocolate to scratching a itch, yet, again, Scripture does not teach that the marriage bed is unclean, nor (by extension) that anything that gratifies the flesh must be sinful (cf. Col. 2)
The imbalanced tradition on marriage versus celibacy led to the belief that clergy were to be single and practice continence even if married, or single or widowed ones could never marry, yet married pastors with children was evidently the norm in the NT church, (1Tim. 3:1-7) with the only known single pastors being two traveling apostles, and who yet had the power to marry. (1Cor. 9:5)
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