You are thinking in the ultimate still....Purely from the position of right and wrong or "draw a line in the sand" point of view. You are making something that is about your son into something about you.
I am going to tell you...parent to parent....Pick your battles. You are truly getting wound up about a six year old's library book. That is small stuff...big time small stuff. Now you can fight a war with your son now....get angry....maybe smack his butt. All under the guise of "He will learn my way, go about doing things my way, and he will respect me". Sorry brother....that isn't respect...That is eventually living out of fear. Then when the day comes that he gets into real trouble....He won't trust you to come and talk about the issue.
Believe me B....I did it just like you. Our pre-bomb house was just like yours. My son kept having issues...and eventually the issues turned to stuff were he could really get in trouble. He wouldn't talk about it, because our relationship was based on control and punishment....not love, trust, and respect.
How I would handle the situation now (understand hindsight for me....my kids are older now and in the day it would have been exactly the same as you did). The look request was already done (give directions once unless re-asked to give them again), I would then help the son look for his book (it is a better use of your time to help look for the book for 5 minutes than spend 5 hours being ticked off), state to your son that you are disappointed he did not get the book himself (You are disappointed....but you let that turn to frustration and anger), I assume this is a school story book and not a math textbook so I would tell him that if this happens again he will no longer be able to bring home school library books.
1) Request once - He has the choice to do it or not
2) Help finish the job if not done -No need to stress for hours over what can be solved in minutes
3) State how you feel about him not doing the job quickly
4) State consequences of what is going to happen in the future if this happens repeatedly
Do you see DB in how I would handle it bud?
As for your wife's response...Once again this is small stuff. Are you willing to go to battle with your wife over something your son did. Yes, some will say it was your wife's response and I will say BS all day long. This is about your son!!!!
The only thing I ask you to think about in regards to your wife...Is that you want to respond in a Sheldon way of right and wrong. Now isn't that something we are working on?
