"Slippery slope," in a sense, only really applies when the slope is steep enough that its slipperiness matters. In particular, there is an obvious difference between "I've discussed problems like this with someone who knows the material" and "I've studied exactly these questions and their answers for the last week."

In the former case, having discussed the material, one is still required to apply one's knowledge in order to produce correct answers on a test. In the latter, one need only reproduce from memory answers one doesn't (necessarily) understand.

I don't think that's the slippery slope part. I think the slippery is not WHERE the test/information was procured, but HOW it was. If they merely bought the teacher's textbook, then it's not cheating. Even if they knew most of the exam's question came from that textbook, it's not cheating. It's lazy, and doesn't foster real learning, but it's not cheating. To me, this isn't a story on cheating, this is a story on laziness, and what acceptable level of laziness is allowed in higher education.