"The teachings of the Church on sex are extremely outdated and unrealistic for the modern world. Why do I need old celibate men telling me what to do in bed? I believe in sexual freedom"
Indeed, some in the Church have been guilty of spreading a backwards and incorrect view of sex; calling it dirty, to be despised, and fundamentally bad. They are misguided and have no idea what the Church teaches.
The opposite is true; for this Church teaches that God made sex, and all that God made is good. It is a thing of such beauty and glory that God chose to have the very creation of each of His human creatures be a consequence of this act.
No religion exalts properly ordered human sexuality like the Christianity does. From the very beginning of the Bible, God blesses as "very good" the intimate union between man and woman. Therefore the marital embrace is obedience to God's Will and is a physical expression of the total gift of self with which spouses bless each other. Each performance of this sacred marital act is a renewal of wedding vows in what John Paul II refers to as “the language of the body.” This marital embrace, in its physical exposition of the difference and the complementarity of the sexes, reveals that same truth on a spiritual level. The woman was created with an empty space inside of her; reserved for the creation of new life and which she gives to her husband in marital intimacy, as they both recognize, using the language of the body, their true completeness resides in only each other, as a communion of persons in accord with their creation. Eve is for Adam, and Adam is for Eve.
Because the Church recognizes the beauty of sex more than anyone, she protects this beauty more than anyone. She never fails to condemn a desecration of it. She implores her children not to reduce it to a mere object of immediate sensual gratification. Yes, it may be hard for some to hear that sex is reserved only for marriage (which must be lifelong), that all sexual acts must be open to life - un-contracepted, that you must never degrade your body with masturbation or degrade others and yourself by viewing pornography, and that certain tendencies (like same-sex attraction) can never be indulged.
But there is not a soul alive born without the knowledge, deep in his or her heart, that these teachings, however hard they may appear, are true. There is nobody alive who does not feel that most terrible pain that exceeds all other pains -- that is, the pain of guilt -- in his heart when in his life he first begins to commit these sins. If you are presently committing them, all you need to do is recall how you felt when you began, and you will find this is absolutely true. There is no way to chalk this up to societal conditioning: society can never cause the real sensation of guilt to arise in the soul; only, at most, embarrassment and avoidance of being caught. And yet, when you laid your head on your pillow at night as you began using sexuality outside of its one and only licit use (marriage), you were, it is certain, filled with remorse.
It is easy to judge the nature of a thing by its fruits; therefore it is easy to see the deadly poison behind the carefree disguises of so-called "sexual freedom." Ever since the modern West has adopted a permissive attitude toward sex outside of marriage, contraception, divorce & remarriage, pornography, masturbation, and the like, culture has steadily disintegrated. Depression runs wild such that an enormous percentage of the population even is prescribed medication for it. Suicide among youth (almost always the result of a sexual relationship gone bad) has grown so astronomically that it is now their leading cause of death. Broken homes have become more common than healthy families with a mother and father. To be frank and honest: western civilization is miserable as a result of our failure to understand God's design for sex. But you don't have to let this be your fate as well.