I really wish someone like you would have told me all that shit when I was a newbie :-)
Which is why I am so adamant about it when I get caught up in a conversation with someone that says something like:
I don't want to diss you but are you from another planet?
The invoice number? A Bitcoin address is more like a customer ID, which remains fixed!
The newbies need to understand just how important it is to use a new address for every transaction. If I don't refute such statements, then many MORE newbies are going to be wishing later that someone had explained the importance of avoiding address re-use, and wishing they hadn't listened to the person that stated that an address should remain fixed.
Additionally, by voting with my dollars (refusing to do business with ANYONE that asks me to re-use an address to send to them), I make a difference in the marketplace helping (forcing) more merchants to learn the importance about protecting their customer's privacy. Those that behave appropriately gain more business from me (and others like me) and are therefore more successful. Those that don't behave appropriately suffer a lack of business from me (and others like me) and are therefore less successful until they learn.