No, there is no forum rule that you MUST respond to a poster’s question.
But one must be willing to dialogue in order to post here.
Many a poster has been banned who made it clear that she was unable or unwilling to engage in discussion.
The general culture here, frobert is this: you pose your opinion. People respond to it either by agreeing with it, disagreeing with it, or asking you to give some support for your opinion.
When people disagree with you, a mature individual does not take it personally.
When people ask you to give some reasons for your opinion, it is part of forum etiquette to respond to their request.
When people ask you to support your claim (let’s say you say, “A pope once said that Mary was a goddess!”), it is not good form to say, “I don’t really care if you don’t believe me! That’s what I was once told. If you want to find out, google it yourself!”
Note: I am not saying that you are an example of any of the above.
I am simply offering some examples of what is good form and what is not.
If you post here, however, please be prepared to have some folks disagree with you. Some folks will agree with you. Some folks will ask for more information.
It is good etiquette to respond.
It is never a mature thing to leave in a huff because someone asked you to support your claim or opinion.
In fact, you are commanded to support your beliefs by the inspired author.
(Who is
not someone one this forum.

)