Pleasure & sex have value if they serve the true and final good (and intended end!) of the soul, specifically by unifying the soul (which has a body, mind, will, passions) closer to God, and that means His will! 

No action is good if it simply serves itself!  Not one

Human sex must be "higher order" than animal sex.  The mind, the will, the soul, the body, its passions & appetites all must be made coherent with a pure intention to love & serve God.

Sex is so much more than the "free sex" generation understands it to be.  This site is a perfect example of "shrunken joy". 

From CS Lewis's profound work:  The Weight of Glory:

“It would seem that Our Lord finds our desires not too strong, but too weak. We are half-hearted creatures, fooling about with drink and sex and ambition when infinite joy is offered us, like an ignorant child who wants to go on making mud pies in a slum because he cannot imagine what is meant by the offer of a holiday at the sea. We are far too easily pleased.”