I agree that it is possible to learn Kitesurfing without lessons - after all all the riders at the beginning did this. However, lets just say that you get your mate to teach you how to get up on a board and get going - that's great. But what about when it all goes wrong? did your mate tell you how to do a deepwater packdown, how to make decisions about whether to deflate your kite or not?
I had a leading edge blow out on me the other day and had to do a deep water packdown then swim back - it was the first time I'd done it since my lessons - It was a long old swim back and without knowing what to do it would have taken longer - maybe I would have lost some kit out there - or maybe worse.
There is so much more to kite surfing than just the technique. I used to landboard for years before getting on the water - and I rate the lessons I had highly.
So what I'm saying is lessons are definately not a waste of time, you can do without them - but the piece of mind that lessons give me - knowing I can tackle many (not all) situations, certainly helps me enjoy the sport more.
Anyway - whatever you do - good luck mate and have a blast doing it