Which leads me to the remaining question, which is: Are Sam's powers actually evil, or begat in evil, or bequethed by evil? Or are they something intrinsic to Sam that Azazel wanted to tap for is evil purposes - and failed - and Sam and Dean simply *fear* that it might be evil?

Thank you! I never understood the automatic assumption that Sammy's powers were evil. Being able to banish demons doesn't seem to be a bad thing, or a power a demon would particularly want to have. I've always been of the belief that Sammy's powers were intrinsic to him. Why would Azazel just pick random kids to give powers to? In that case he could have given them to anyone, chose all orphans with no ties to society who are a lot easier to manipulate, but each child he picked seemed to be very specific.

Sammy could very well become a god-like force of good. The powers are a tool, what he does with them is up to Sam.