What is really evil is that Norman comes in like a dutiful son, and cleanses away the evidence. IOW, the wicked cleanses away the evidence of sin instead of trying to cleanse away the sin. All of that from the shower scene and its aftermath.
I think the particular point above is nifty and "new to me." In other words, I've read a lot of writing over the years about Marion's shower being meant to "cleanse" her (I suppose of sins, but more on that in a moment), but I've never really heard the extra distance of NORMAN cleansing away the evidence of sin -- and, hey, its a BIG sin: murder most foul. The taking of an innocent human life.
Marion's shower has also been described as a "baptism" but to me that's a matter of re-birth rather than cleansing. It just goes to show you: one great symbol(the act of taking a shower) can be given several different interpretations.
Now, about Marion's "sins." The New Yorker critic who hated Psycho, Dwight MacDonald wrote something like "there's an unpleasant Hays Code puritanism to the shower murder: see what necking, thieving girls get." Point being that Marion perhaps DESERVES to be punished for pre-marital sex and for evening THINKING of stealing the money(even though she decides to give it back.)
I doubt that Hitchcock saw it that way. At all. On the matter of theft, its a matter of irony: she went "a little mad" in taking that money, she wasn't a criminal , she did it for love. And she dies anyway. But WHY does she die? Because she sought to take the money to Sam, in Fairvale, and got waylaid 15 miles away at the Bates Motel. In short, she died over Sam's location, not the money.
On the matter of the "pre-marital sex," well, being a 1960 late Hays Code movie, Psycho doesn't show these two having sex. It is implied only, and maybe they WERE only "necking in their underwear" (which strikes me as ridiculous.) It is key that Sam is long divorced -- this isn't adultery even by 1960 standards.
I would suggest this:
By setting up Marion Crane as single, "carnal"(in a good way), and capable of criminal action(even if "mad"), Hitchcock created in Marion a "noir female" whose horrible death in that shower at least felt like it was happening to a woman who...took risks, walked on the wild side.
What if Marion Crane were a happily married, sweet mother of two on her way home from a business trip to return to her loving husband and two little girls? THEN her murder in that shower would be a true outrage against humanity even beyond the horror that it already is. But show her as childless, sexual, criminal...sort of...and suddenly it seems a little more "inevitable" (but NOT fitting) that she ends up in that shower. You only turn up at the Bates Motel if you have taken "the wrong turn."
There is also the issue that the Marion Crane who shows up at the Bates Motel has been rather banged around by life anyway. Parents are dead, not married, let alone with children, dead end job for 10 years of her young life already. As will happen with Richard Blaney(not getting killed, but getting framed) in Frenzy, it is as if hard financial times render a person vulnerable to all manner of danger.
I didn't think of Marion as a "noir female" from her introductory scene. She is wearing white as symbolism, is an adult, so premarital sex isn't that big a deal. I think even before the 60s, the Hays code was being stretched as more explicit foreign films were being made, so audiences wanted to see them. Hollywood had to compete and filmmakers made more risque and explicit movies. The following lists what we see in the movie, i.e. plot keywords, https://www.imdb.com/title/tt0054215/keywords?ref_=tt_stry_kw You may find interesting safe sex, proto giallo, foot closeup, all knowing psychiatrist, and breaking the fourth wall. You should especially enjoy the last two I took out.
Just to clarify the adultery, for Christians, Jesus said that someone who marries, divorces, and gets married again or has an affair is committing adultery. This is Sam Loomis. Not Marion. The only exception is if there was adultery involved by the spouse during the original marriage. I guess we do not know that, so Sam may have an out. That said, like murder, grand theft, and other sins, one can be forgiven. I think with re-marriage, one has to be certain that the second marriage will last. Jesus was referring to getting married as "until death do you part" or else it is a sin. One has to repent the first marriage and not let what caused it to fall apart carry on into the second.
The second part, I took the liberty of injecting in there if we are discussing sin. Normally, we do not think about sin. Isn't that what sinners do? They deny their sin. They pass the blame away from themselves. They may end up blaming God for the circumstances. They aren't willing to accept the sin, so they want to cleanse away the evidence of it. Even Mother does this to Norman at the end.