I'm not sure if the folks claiming harassment, death threats, and various kinds of -phobia are unaware that it can be difficult to conclusively connect the dots on these things or if they ARE aware and are deliberately taking advantage of the ambiguity.
The "report" feature on vBulletin, phpBB, and other sites preserves the chain of custody on the message. An admin or mod can see that, in fact, user X sent user Y a death threat. That doesn't prove, however, that user X and user Y are different people or that user X is really user *Z* (that takes a whole different level of sleuthing), but you can at least establish that a threat was sent and user X did it.
If people on G+ and elsewhere are getting death threats related to this controversy, they should be using whatever official report features are available to them. Anybody who's been on the Internet a while knows that fake reports are a thing, and that's why it's important to preserve whatever chain of custody there is. I understand that it's maddening to get a shitty message from JoeBlowAnonUserX and be unable to prove that your sworn enemy is behind it. Even someone with a decent level of system access and technical chops can struggle to make that connection. It can be done -- if the stalker is stupid enough (mine was hilariously so) and if the person doing the reverse-stalking has a few skills.
I've said here before that I was threatened and stalked on rpg.net and a few other places by the same person, and I haven't publicly posted who did it. One reason is that doing so would reveal technical measures I'm quite happy keeping to myself.
Another is that I may yet have to take legal action if he ever starts bothering me again. And finally, because I am not prepared to upload a metric assload of technical data, thereby exposing not only my technical methods but also the identities of people who helped me nail this guy, I won't reveal his real name and socks publicly. Unless I'm prepared to lay out the *full* case (which I haven't yet to anyone other than family), I'm not comfortable naming names in public.
Making these accusations against Zak and Pundit without conclusively backing it up is a credibility-damaging move -- for the accuser.