“Herd immunity is a theory that was never proven.”
Putting aside the fact that that statement is false (though ot be fair it depends what you mean by “proven”
that in no way answers the question.
The question wasn’t “Why is it that pro-diseasers not accept herd immunity”
In which case your point would be relevent (if it was true).
The question was “Why is it that anti-vaxxers need to have herd immunity explained to them every single time?”
In every discussion Ive had wit h people “who have done their research” both in person and online, this always comes up. There are p[probably dozens of threads on ywn I’d bet that every one has some pro-disease individual asking “why does it matter what I do if your’re child is vaccinated?” or something to that effect as if they thought of some briliant question that has never been asked before