The fact that a post is public does not mean that every response is justified.

Publicness establishes an opportunity for criticism, not the correctness of every possible criticism.

For example:

“I disagree with your historical interpretation.”

is legitimate criticism.

But:

“You are an idiot and everyone who agrees with you is stupid.”

is not made intellectually legitimate merely because the original post was public.

Likewise, harassment, threats, repeated unwanted contact, or disclosure of private information cannot be justified simply by saying:

“You posted publicly.”

So the principle should be:

Public claims are ordinarily open to public criticism, but the right to criticize does not justify harassment or abuse.