I understand that mentality. I too used to give the side-eye to people with decks full of proxy cards, but as I've grow up through the game, amassed such a large collection of cards, and the prices of the older ones that I'm missing have taken to new astronomical heights, I've outgrown that way of thought.
As an example, I had a fun deck idea that required a play-set of
Invoke Prejudice. At Star City's bargain basement price of $99 a pop, there was no way I was going to blow $400 on four cards for a deck idea. Especially since the deck is not terribly competitive, there are almost no sanctioned Legacy events in my area, and I don't think I've ever physically seen more than one
Invoke Prejudice in a store at a time so trading for them in a hurry was probably out of the question as well. Fortunately, three minutes, a printer, and some scissors later I was able to slide four printed proxies into my deck and play a few casual rounds with my friends. We all had fun, nobody got pissy, and after I had my fun I took the deck apart and moved on without having burned $400 to have some old cards sit in my binders.
From Wizards perspective, everything was a win. They weren't going to make any money if I bought the cards or proxied them. Everyone played Magic and had fun. No sanctioned tournament rules were broken.