I am always fascinated by this discussion.
Let's spin this out a bit. Let's say that we can all figure out a way to take PADI (or any other certifying agency) courses without paying for them. Eventually, your certifying agency goes out of business because nobody paid for the service they offer. I mean, it's just knowledge right; that has no actual value once it has been transferred once.
So, your certifying agency is gone. And one day you spend a couple thousand dollars to travel to some exotic destination to dive and the shop there declines to fill your tanks or rent you gear because you are no longer certified by an existing agency.
That is not a farfetched scenario.
Personally, I think these kinds of discussions truly go to a very fundamental concern. If someone is willing to cut corners on something as basic, and cheap, as course material. Then there is a real question about their willingness to be safe when it comes to the far more expensive proposition of dive gear, and the safety inherent to making the right decisions on the purchase and maintennance of that gear.
In my opinion, dive instruction is incredibly inexpensive. Dive instructors clearly do it for the love of the sport. The course material costs practically nothing compared with other activities of comparable nature. Not to mention, there are so many certifying agencies for diving, unlike activities such as sky diving and flying. That competition seems to keep the price low.
If someone is unwilling to pay for a book, how can I trust that person to have the necessary equipment to be my dive buddy?
I don't mean to offend here, and I understand there are varying levels of financial ability involved. But by the same token, I have never heard anyone say "I'm an unsafe diver because I can't afford to be a safe diver...but I'll dive anyway."
A final point: Personally, I would like to see my certifying agency continue in business. Just like I want to see Adobe continue to come out with new versions of Photoshop. For that reason, I am willing to pay for the services both offer.
Again, I hope I haven't offended anyone here.
Best wishes and safe diving.
Jeff