This is purely speculation and does sound a bit crazy but I think he's just following the play book they give you when you join the anti-vax cult, which is one of several movements that has been hijacked by what is, at it's core, an antisemitic movement, that has been organising around the world, hijacking every cause that they can get a foothold into.
They are well versed in manipulating people into joining their groups, and creating a cult like environment where your identity is tied to the group, where your membership of the group causes you to cut ties with family and friends or them to cut ties with them, leaving you ever more reliant on the group - which gives you validation and support when you do the right thing by them. They are good at manipulating people, they are good at organising people and they are good at propaganda.
They have turned the "but" from "I'm not racist but..." into an art form.
"I'm not antivax but...I don't want to tell anyone my medical history, I have a certificate from my doctor, the government shouldn't be able to force me to do things".
Arguments that sound reasonable when taken in good faith but they are rehearsed and scripted and they will change their story to suit the audience. No one wants to just call them out on it and that's what they are relying on. The Eagles and Colin Young expected Darling to come to his senses but the antivax group are cheering him on and treating him like a hero, instead of lecturing him about how stupid he's being and the adulation will get stronger because they will know, because we've seen it with Cousins and Kerr and such, that a large number of West Coast supporters will change their previously held beliefs to justify why one of their players isn't in the wrong.
He's a recruiting tool now. The Eagles should denounce him and cut him loose.
