I don't disagree with anything you wrote.

If there is not a worthy academic willing to present the viewpoint, then such viewpoint need not be represented.

However, I think there is risk to calling certain things "settled" as a way to stifle dissent or chill contrary research. For example, I don't think universities should exclude communists even though it's fairly settled these days that communism has not worked in practice. Likewise, I don't think universities should exclude climate scientists who are skeptical of the current models of anthropogenic climate change.

Personally, I think the harder questions are ones that involve certain ethical questions. For example, should (and if so, to what extent) universities allow research related to the genetic modification of human beings or the creation of cyborgs?