Not because it isn't true, but because it's used as an excuse to justify an arrogance that can only come from ignorance.
It's essentially saying: "Everyone has a right to come to a false conclusion." False by virtue of being premature.
There are very few experts and fewer unquestioned authorities on the complex human issues upon which we form, or more often, adopt, our opinions.
And those who have really wrestled with the nuances of complex issues and acquired an informed opinion realize that they are not experts, much less, authorities on the subject.
They realize that their opinions are insignificant and provisional. They never end discussions by announcing their opinion. No, they make a particular inquiry, based on knowledge and curiosity, desiring to expand their understanding.
So I'd rather we said, "Everyone has a right to ask questions." Or "All questions are welcomed." This would encourage inquiry and discourage the feeling that we should know stuff when there's way too much stuff to know, but together, we know a lot.
This is harder, I think, because questions betray ignorance, whereas ignorance is concealed by opinions.