said by John Galt6:3 - That's your opinion.
4 - It's not "clearly unsafe"...it is a violation of the Code, however.
5 - Sure you do...a (now removed) attic-mounted HVAC unit could require a 10/2 for the unit and an 8/2 for emergency heat.
3 - It's also the opinion of the forum moderators judging by the number of threads which get locked and/or deleted. I'm really surprised »
Wire Size didn't get locked; »
Improper ground most certainly did.
4 - That's your opinion. It's clearly unsafe to me. The "doubling up" for the neutral and ground kinda reminds me of that now-deleted thread of someone asking something similar which ended with 4 pages of arguments about exactly how unsafe that was followed by the deleting of the entire thread.
5 - Unlike adding A/C to a furnace, electric emergency heat is built into the main HVAC unit and doesn't use a 2nd circuit. While having both an unused 8/2 and 10/2 ending up in the same place /could/ happen, I find it highly unlikely.
/M