If ET came

First and foremost, there would be chaos. Most people stay respectable not because of fear of government but because of deep rooted religious beliefs. God keeps most people in check. Fear of eternal damnation, judgment day, justice by a higher power. A power deserving reverence in every sense of the word, a greater being… the Creator. Most of the major religions are people-centric, obviously. We are created in His own image, we have been given responsibilities, we have to honor that power. It is that fear of Almighty, omnipresent being. Of course, we know that it is bad to hurt another human being, but its not enough. If there was no fear of God, the fiber of our society would crumble from the inside out. We have not yet reached that stage in our evolution where logic would dictate over our self-interests. We can’t think in terms of a hive. We may never get there. That is why religion is necessary. It forces us to stay in check because even when no ones looking, God is still watching us. And we would be judged for our actions as well as inactions. He can punish us whenever He wants, we will never come to know it. It could be tomorrow or generations down the line but justice would be done.
So if ET did come around, it would be catastrophic. Not only would we be not alone, but there would be something there greater than us, and not created in the image of the One who created the universe. We know God looks like us, we are sure of that. And if that is a contradiction then how many other contradictions are there? If the beginning is wrong then there is little chance for the rest to be right. There would be a deep identity crisis and societal restraints would literally rip. Humanity would not find a moral equilibrium but continue further down to our darkest recesses. The eons of continually hammered obligations would break out without any control. We would become animals and jungle rule would dominate every aspect of our life.
God has been so deeply indoctrinated into our lives that we no longer have the sense to look at morality from its logical and beneficial point of view. For the sake of the common good. We do right because God commands it. Had He not, we would put our own self-interests first, always. While we can circle the globe in a few hours, we can’t look inside our own hearts and decide on right and wrong. It has to be spoon-fed. This makes it easy to keep the masses in check but it can also be a double-edged sword. It can be manipulated against humanity itself. Either way, keeping in line with the present topic, the existence of an intelligent alien species could really create a mess of things here for us. No intelligent race would wish that on poor us.
And that is why an ET can never happen. There’s miles of evolution still left to go before we are ready for such a shock. I am sure they understand that too.