If we're only ever allowed to change our minds by a little bit we'd all be struck in the neighbourhood of whatever (silly) opinions we had as five year olds.
Also, who's in charge of deciding what constitutes a 'complete' mind change vs the apparently-ok minor mind change?
If you want a fair discussion of theories you can’t label the other one a conspiracy theory.
So, should they be able to change their mind? Sure. Should they be less dismissive of opposing views? Also yes. There's no contradiction there.