Blame can pretty much be pinned on anyone if someone tries. We all know that Tara is NOT the cause of Willow over use of magic, Tara is one of the reasons she stopped. If other people don't see that then that's their problem.
I also agree that its not all Amy's fault. I definitely think that if anything she was a catalyst. and I also agree that I like Amy's character in season 6 because even though she tried to get Willow hooked on magic again, she's a cool kinda evil. A not really evil evil that is more meaningful because she's been on the show for such a long time. technically she's actually only been in a few eps, but her presence has been there since season 1.