Sin makes us stupid. How?

I’m not a psychologist but that’s not going to stop me.

I think it’s because we have to negotiate with ourselves in order to permit ourselves to commit the act in question without remorse and penance. In order to do this with a clear conscience we must deny a truth. Once we allow ourselves to deny a truth because we want to in pursuit of pleasure or retreat from pain, it makes it easier to deny the next based on our desires. Each time we do this it gets easier and less painful to do so.
In this way, while subjecting our intellect to our emotions, our conscience and logical abilities like a piece of tape having been ripped off over and over again loses its stickiness until it will not stick at all. The sacrament of reconciliation helps us put some stick back on the tape if we keep humbly admitting our errors.
Without reconciliation we then become emotionally tossed creatures with no compass outside of our own emotions and wants allowing the complete take over of our intellect by our emotional appetite for our “needs” to be satisfied. The idolatry of self is completed then as the one true God has been supplanted by the god of our feelings. Having put our hope in the comforts of the flesh and happiness in this life above all, our fear of Hell is replaced by our fear of not living our lives to the fullest desire of our hearts. Having no hope for our eternity, death and personal suffering is the greatest injustice although it is through death and personal suffering that our God provided mercy and resurrection. We reject our way of the cross and decide that we will not follow Him if it means self denial.
Our faith in Him is snuffed out and replaced with faith in government or other authority figures, who as our new saviors, will help us enjoy ease of life and indulgence of pleasure and because they promise to save us we have irrational faith in the things they tell us no matter how ludicrous.
Once this happens, having someone hurt our feelings, or the feelings of a group by confrontation of our carefully crafted narratives creates a victim of that person or that group. These hurt feelings then become the only remaining form of blasphemy accepted by the darkened intellects those who have embraced logical deviance in favor of their own fickleness.

In this condition, one is unlikely to escape unless they discover the pain of their selfishness and their darkened intellect is infused though God’s mercy with the light of grace to see their error. Many do see it, but still choose (due to ego or the difficulty of making amends) to turn the light back out rather than go towards it, opening themselves up not only to manipulation by their own feelings but the overarching influence of the demonic. They have progressed to the stage of being used as a tool to actively darken the intellects of others through actual widespread promotion of sin. The feeling of being “legion” in their error and having others join them in the suppression of truth gives them a sense of legitimacy and the correctness of their feelings because of the strength of their numbers. Teens and young adults with their new found freedoms are especially easy prey in this respect as their friends who are equally in experienced in dealing with their own thorns of the flesh and the pain caused by the thorns are a ready made legions of their own. Once sucked into the supportive lies as a youth their intellect is darkened before experience is gained to combat it and the door of what could be their life long prison is closed.
When a large enough group of openly darkened intellects is assembled, they will predicability endeavor to crucify the Truth because they can’t bare the sight of Him who reminds them off their lusts if the flesh.

In my personal experience, the only way to escape is by humble submission to truth, rejection of the elitist culture of reason corruption through an absolute rejection of moral relativism, penance (like going to the gym) to train our will to be submissive to the truth, lastly and most of all the grace to desire it as it is culturally expensive to escape when the culture has no desire to do so.