“If you post something publicly, everyone can respond”

Here again, there is an important distinction.

If someone deliberately makes a post public, they are making it available to an audience. In ordinary discussion, that creates a legitimate opportunity for others to:

• agree;
• disagree;
• criticize;
• correct;
• question;
• rebut; or
• add qualifications.

So your basic point is sound:

Making a statement public does not give the author control over whether other people may intellectually respond to it.

But this does not mean that everyone has an unlimited entitlement to respond in every possible way.

For example, the author can reasonably say:

“Please don't contact me privately.”

or

“I don't want to debate this personally.”

or, on a platform they control, they can moderate comments.

Those are different from saying:

“Because I made this public, nobody has the right to criticize or rebut it.”

The latter is much harder to justify.