Now perhaps the rule should be tweaked to say "intentional and unnecessary" before a penalty is applied
Agreed. This was going to be an intentional and calculated swatting on my behalf if that disc didn't start to flex. I was two steps away, I saw the throw, I saw it flip, I took a step closer just incase. Last thing I need is to let him get hit and get sued for failing to be a good samaritan or more realistically being known as the guy who let someone else get driven to the noggin while I just stood there arm's distance and watched.
I'd hope people understand the purpose and not worry about the rules like that. If someone calls me on that and tries to apply a penalty, my next drive is going towards their head and I won't be there to block it.