Ever!  You are not even entitled to "I don’t know."   You are entitled to your desires, and sometimes to your choices.   You might own a choice, and if you can choose your preferences, you may have the right to do so.  But your beliefs are not about you; beliefs are about the world.  Your beliefs should be your best available estimate of the way things are; anything else is a lie.

If you ever feel tempted to resist an argument or conclusion by saying "everyone is entitled to their opinion," stop! This is as clear a bias indicator as they come.   It may irritate you to give in, but honesty demands it.    

Yes, you can sometimes reasonably reject a claim that appears well supported by  arguments.   After all, a reliable source might recommend against the claim, but not give its reasons.  Or the arguments might come from a biased source, good at searching selectively for arguments favoring a certain side.  But beware the temptation to use these as blanket excuses to ignore good arguments.

The idea that everyone is entitled to their opinion comes in part from our cult of democracy.   We are proud to live in a society where we all can "have our say" by talking and voting, and those who claim we do not know enough to have a useful say, we suspect are trying to disenfranchise us.   We must therefore all know enough to have a useful say on any public issue.  But that is wrong.   

A related error is the idea there are two kinds of topics: facts and opinions.  On facts you can be wrong, so you just go to experts and then believe them.   On opinions no one can be wrong; the weight of opinion is the weight of power; those who say there are experts are trying to trick you into giving up your power.

My students don’t expect much class discussion when I teach math or physics, but they do expect discussion on topics related to personal choice or public policy.  And they expect any opinion expressed eloquently and with passion to be worth as good a grade.  (At least non-economics students expect these things.)

Jared Diamond writes:

Anybody, scientist or no, feels entitled to spout forth on politics or psychology, and to heap scorn on what scholars in those fields write.  

It is true that some topics give experts stronger mechanisms for resolving disputes.  On other topics our biases and the complexity of the world make it harder to draw strong conclusions.  And topics where most of us can contribute relevant information may be good topics for discussions, and not just lectures. 

But never forget that on any question about the way things are (or should be), and in any information situation, there is always a best estimate.   You are only entitled to your best honest effort to find that best estimate; anything else is a lie.   

Added: M Lafferty points us to this similar article by Jamie Whyte.