No, that is a complete overreaction. You can still call out "aliens did it" or other obvious nonsense.
You made a category error by somehow replacing "opinions which are obvious nonsense" with "any dissenting opinion whatsoever".
Nobody but you suggested that. The claim was that you cannot say anything at all about any "dissenting opinion" unless you are 100% sure you are correct. That is nonsense. You can obviously say something about some of them, while not being confident enough to rule out some others.