I started AD&D with photocopies of the books. That's all I could afford for a time in my early teends but then I bought everything in sight once I had an income. Yes, it was piracy but I've been a customer for 30+ years so it's worked out OK for TSR/WotC.
Honestly, what you just described, I don't consider that piracy. First, you copied it... it's not like you actually stole the books off a shelf. Second, you didn't sell your copies, so it was for your personal use in gaming. Third, the borrowing/copying you did then led to decades of actual purchases. I don't see a single thing wrong there. Remember also, when the AD&D books first came out, they didn't expect every single player to buy/invest into a complete set of books, and many things were designed to be copied and shared.
In this new day and age, lawyers and corporations want us to believe that sharing = piracy, that sharing = stealing. But 95% of the time, it's not. It's just a case if personal use, in a game that is fostered by sharing and cooperative play. Imagine if we lost our public libraries, or were required to buy memberships to get through public library pay-walls for simple things like novels or journals.
I do think, however, that the current WotC approach is completely and utterly mindless. Now, that's a fairly strong expression so before the mods slap me for it just let me explain.
Let's compare and contrast WotC with Paizo.
WotC doesn't sell PDFs anymore because the lawyers, presumably, won the internal argument that selling PDFs encourages piracy. The net effect: PDFs are not available for legitimate sale but practically the full library of every edition is available for free and easy download on the 'net.
Paizo, by contrast, sells PDFs. They also have sensible pricing on some of their PDFs. Are they pirated? Yes, but to a much lesser extent. And why is that? Because they not only build some really clever security features into their PDFs but they scour the internet on a daily basis to make sure that pirated copies are taken down ASAP.
WotC has simply not followed through and I am grateful for that because I can get PDF copies of the books I have bought - yes, I buy the books - without having to waste my valuable time scanning them. Thanks, WotC! You've saved me money because before I bought the PDF also.
I do like the Paizo approach as well. I like having my books at home, for times when I want to sit and read something physical. But when I'm actually gaming with others, I much prefer having PDFs or other types of electronic versions on my iPad or laptop. I can quickly search things, don't have to fumble with 4-12 books and possibly spill things all over them, and best of all I can travel light to the DM's house.
Back in the days of AD&D, especially when I was DMing, I had to carry a ton of books around for reference and player use. PDFs are something the electronic age did correctly. Even for work, I love getting electronic journals and books online. I can take a break at a coffee shop and read my science journals... I can take a library of things with me to a conference, all on a tiny iPad or even my phone. Best of all, if I need to send something to a colleague for collaboration, editing, or content review, it's far better sending a PDF or doc than going through the hassle of photocopying something and shipping it via regular mail, or hoofing it.