"For the most part, high-profile "targets" from the troll's perspective are already known to the public anyway."
I think the author was simply pointing out that well-known people are well known, so their privacy is, almost by definition, limited anyway.
That people who have some level of public exposure (as you and I do, posting on a public forum) will have some personal information out in the open is obvious. The thread-starter appears to be playing down the damage that doxxing can do "I do want to gently call into question the danger of the attack surfaces". To me, their admittedly unspoken, conclusion from point 1 is therefore "they had it coming".
In this case, the one with which you seem to take issue OP's point #1, which I merely want to point out is a surface that is only available against people who haven't already dox'd themselves. And for those people - people who want to occupy a place on the anonymity spectrum that is far away from a "public figure," the threats to this attack surface are more damning than trolls - they include huge advertising corporations and the NSA.
FWIW, immediately before that sentence, the thread-starter called into question the real danger of doxxing and calls to "action" based on the released information/misinformation.
I did not at all mean that. What I meant was that doxxing is a complex attack surface. If someone is already high-profile and public, they can't really be dox'd. If someone isn't, then staying anonymous is a more harder task than avoiding being dox'd. That's all I was saying.
If anything, I think that people who choose not to be anonymous need more social / political support, not less.