One may reasonably debate whether someone who did something bad in the past should be ostracized, but I think you are rather mischaracterizing the author’s argument.
This is what the OP literally said in the opening paragraph.
On the contrary, having never been found guilty of anything, the bar for forgiveness / rehabilitation should be even lower. If it is a basic human right to be rehabilitated back into society even if they have been criminally convicted, it should certainly be a human right if they were merely "convicted" by an academic kangaroo court.
Society hasn't exiled him into the woods, people are just rightfully exercising their right not to be associated with him.
No, they are harassing a person who is exercising their right to associate with whomever they want.
To associate with, that is the part that matters. Not "to be associated with", which is what people in a mob think is what matters, even though it does not, certainly not enough to give them license.
Harassing is carrying a _ton_ of load, way above its capacity, in the essay. I'm very curious for your perspective on what incidents were harrassment.
There's a certain motte-and-bailey aspect in my read, the narrow claims are their talk on Geoff's work was not accepted at an academic conference and someone removed Geoff's name from their paper.
The broader claims range as petty as the conference added a non-standard tricky clause to harrass them and engineer the denial of their proposal, before their proposal was made (?, also, it's a bog-standard morals clause in my read) and as vast as you must allow anyone to associate with you & it's immoral to decide who you associate with unless they've been convicted of a crime by a jury in the United States.
It suffers from its rigidness and righteousness.