Deleting would be reframed as enforcing censorship or an attack against freedom of speech, and those topics have already been dragged into the dirt around these parts:
Closing topics allow the reasoning to be visible, and it is very obvious what the reasoning is, you already spelled it out for everyone. Unlisting the topic could allow for hidden discussions instead, but then it would not be about Qubes OS at all and start off with a political opening that can easily divide communities.