The reason I'd regard APG's attitude as victim-shaming is that it's turning absence of a virtue into a vice. All credit to people who can bat away criticism, no matter how strong it is, but that shouldn't be equated with "if you are shocked by [the abuse on] a forum don't go on!", or "it's [your] fault for being too open on a forum", or whatever.
In the first place, the correct attitude really ought to be to tone down the abuse, ie for the would-be abusers to take a long, hard look at themselves and accept responsibility for what they post. In the second place, it can be difficult to realise just how open you've been. Even logging into a website (assuming no use of VPN, and possibly even that isn't 100% secure) reveals information about you to those willing to track it down; and, besides, this takes credit away from those desperate to use the tiniest snippets in order to track someone down, or ignores the problem that public figures in particular are more or less obliged to be open.
Finally, the nature of abuse is that how it's perceived is often personal, and it's not clear how such feelings can ever be regarded as wrong. Maybe there has been a recent personal tragedy in that individual's life, maybe the person is ill. Or maybe the threat is actually, to an extent, followed through. Ignoring or invalidating those feelings is, at the very least, lacking in empathy.