> Is it instead the case that you'd have a hard time convicting anyone of hacking-related crimes under any circumstances because of the possibility that someone else might have been pulling the strings?

That is kind of a serious problem. It's like the "open WiFi" defense. It's completely plausible that someone else actually used your WiFi or compromised your computer, but at the same time some people have this visceral reaction to allowing it as a defense because it's so hard to disprove and can be used by anyone.