What’s wrong with religion is it’s irrationality. What’s detrimental about religion is that this irrationality is not questionable.
Imagine, if you will, that someone believes they’re destined to marry Angelina Jolie. They know with 100% certainty in their mind that this will happen. Because they know this, they act accordingly. They volunteer at a local daycare to become more parental and experienced with children in anticipation of raising Angelina’s kids. They learn the different languages of her children to become more culturally aware. They work harder at their job to make money knowing they’ll have to help support her. They conduct themselves in a way as to better equip themselves for their marriage. The things they’ve done are not bad. But they certainly are irrational.
Now, this could easily go the other way. They follow, stock, try to rape or murder Angelina based off of this irrational belief. However, you don’t have to consider the worst case scenario. Even in the best case scenario, where this person is an overall fantastic samaritan, their belief is still entirely irrational. This idea of unfounded destiny, a prophecy to marry Angelina Jolie, is an insane way in which to view the world, even if this view of the world is not detrimental to others. The actions taken were good ones but the reasonings are not an accurate perception of reality.
Now you can consider the worse case scenario. It’s easy to see how something like believing Angelina Jolie is going to marry you can turn ugly and violent. What other objection could you really have to this belief above the fact that this perception of reality is distorted? If, for a moment, you grant that believing a multimillionaire superstar actress will indeed marry you is a good way to view the world, what possible objection could you bring to this view? How could you argue with any harmful behavior inspired by this belief? Say this person wants to kill Brad Pitt in order to annul their marriage. How do you argue with this action given that it’s perfectly fine to believe you are destined to marry Angelina? Through they’re belief, it’s easy to justify the death of Brad Pitt for the greater good. The only real argument to dispel this is to recognize that believing Angelina Jolie will marry you is an irrational belief.
This is what’s wrong and damaging about religion. It’s not the good things religious people do. It’s the toxic things religious people do. If every zealot was a Jainist, religious dogmatism would not be a scary problem. The hateful, racist, sexist, homophobic, xenophobic, ignorant teachings, taken literally, are the core of the problem. All the nonsensical words, of the monotheisms especially, are the fuel for conservative worshipers. If granted that being religious is a rational way to be, how do you argue with the bad things religious people do? How do you argue with Exodus or Deuteronomy if it’s okay to be a Christian? This cherry picking moderation of liberal religion is the best religion can do. In its worst, most literal case, it’s a death cult. In either scenario, it’s completely irrational to believe in an omnipotent, omnipresent deity that cares about who you have sex with and whether or not your men have foreskins. There is no reason to believe or evidence to suggest that a god figure anything like religion suggests exists at all, let alone what exactly the god figure expects and demands.
You don’t need religion to be a moral person. You’d be better off without it all together.