Sex has contributed evil because it's driven by lust in most cases and when you are driven by lust you make stupid decisions and you ignore everything else in life like God, family, community, spiritual growth. Also you can become a slave to lust/desire and you can go to any lengths to fulfil the lust/desire. 

When you are enslaved by lust/desire or any emotion/desire/ego you become selfish and you only care about that lust, desire, emotion, or ego and you stop caring about everything else and that means you stop caring about morality, God, integrity, doing the right thing, honesty, and all that and you lie to yourself and to others in order to fulfil your lust/desire/ego and that leads to all types of immoral, evil, unethical behaviour.

When you are led by lust/desire/ego or any emotion/desire you become self-centered and you think that only your perspective and personal opinion matters and that you are superior to others and you will try to get what you want and impose your opinion/perspective to others without even listening to others or taking time to consider all the angles and points of view of other people and that leads to very immoral, evil, unethical, dishonest, selfish and hurtful behaviour in which others suffer.

When you are led by lust/desire or any emotion/desire/ego you lose your moral compass and you stop thinking in terms of right and wrong because your desires and ego and lust cloud your judgement - that leads to lying, cheating, murder, fraud, theft, abuse, neglect, and just a general lack of care or respect for human life and a lack of respect for other people and their lives because you only think of yourself and your lusts, desires, and ego which makes you selfish, evil, immoral and unethical.

When you are enslaved by lust/desire or any emotion/desire you lose control of your thoughts and you are driven by your emotions/desires and you get lost in your emotions/desires because they are so strong and they have the strong grip on you that you can't even think clearly, logically, rationally and you only do selfish things and immoral and evil and unethical things because your sense of right and wrong is totally destroyed because all you are thinking about is how to get what you want in that moment instead of having self-control, a moral compass or thinking about other people.

When you are driven by lust/desire or any emotional/desire/ego you don't care about anyone else but yourself and so you are willing to do anything - even commit evil and immoral and unethical deeds just to get what you want and in that state you are willing to abuse and use other people in any way you can and you don't care about how those other people feel because they are just tools that you can use to get what you want and even if the other people are hurt and die you don't care because you only care about yourself and your lust, desire or ego in that moment.

When you are enslaved by lust/desire or any emotion/desire/ego you lose your will power because all you are doing is giving in to your impulses without any self-control and you become weak because you are not able to do the hard work of self-control and instead, you let your desires control you and you spend all your time and energy giving in to those desires and that means you are not able to do all those other beneficial and good things in that time like going to the gym, learning new skills, reading, studying, doing good deeds for others, trying to grow as a person.

Being enslaved by lust/desire and emotion/desire/ego is very bad because it clouds judgement, morality, self-control, truthfulness, logic, compassion, empathy, integrity, right and wrong, etc., and it's all around evil and immoral and unethical and harmful and hurtful and wrong.

Jesus Christ told us "If your eye causes you to sin then gouge it out and throw it away" (Matthew 18:9). When Jesus spoke these words, He was showing how serious sin and lust is. This is why pornography and lust are so dangerous and evil. Because they can pull you away from God and cause you to go down a dangerous, destructive path. It can destroy your life and the lives of others around you. Lust can lead to destruction, shame, regret, guilt, hurt, pain and suffering.