Everyone's heard the phrase "I'm entitled to my opinion", some of you may have even said it. But guess what, you're fucking not. Not always.
Every good intentioned human being will claim they make their life decisions based on reasons, as they all should. You stop at red lights because you know it would be dangerous not to. You don't send the Prince of Nigeria your banking information, because you can figure out it's probably a scam. However many people act everyday according to beliefs that they can't defend, and further more, don't know why they believe in the first place. Worse, some people preach and tell others about their beliefs, while not being able to back them up with evidence.
If someone challenges one of these beliefs in the course of a discussion, they can be met with "Everyone is entitled to their opinion", which stops the discussion dead, and creates a social environment where it is rude to continue to challenge these beliefs. Instead, use of the phrase "Everyone is entitled to their opinion" should be met with roaring laughter and ridicule at the ignorance of the user of the phrase.
Everyone has the right to say and to think whatever they want, but it does not mean anyone has to listen, and those who do listen to opinions of the ignorant, are fools.
An example of this: an economic convention, where the worlds top economists have been invited to speak about economic theory. If a man sitting in the audience, with no economic training whatsoever, stats up and says "I don't like this theory of supply and demand, I don't understand it and therefore it's not possible, it doesn't resonate well with me". That man will be laughed at, and dismissed without question that his factual claim is untrue and invalid.
However another example: Scientists discussing the theory of evolution and natural selection, receive comments from people with no scientific training, saying things like "no, it's not possible it all happened by random chance, look how complicated the eye is, it could not just have happened without intervention from god.". The scientists laugh at this notion, they have studied for years in this area, and can all postulate quite specifically how it happened, and they pity the man for his obvious lack of education on the subject. It's not his fault, we don't all have time to become experts in the field of genetics and evolutionary biology.
The problem comes when this man preaches his beliefs to his friends, family, and anyone who will listen. They also, are not geneticists or evolutionary biologists, and develop this (untrue) belief about evolution.
But what is the problem? They don't effect anyone by believing this. Wrong.
If they teach their children, their friends, this untrue belief, it creates a distrust for scientists. It leads to assumptions about other people who believe the opposite, a politician for example who believes strongly in evolution, will be assumed to be wrong by those with the untrue belief. The child taught that evolution is a myth, is one less child that might grow up to love science, and make breakthroughs that improve the quality of life for people.
Holding untrue beliefs is a problem. Believing things without proof is a problem, you wouldn't go to a mechanic for that lump growing on your neck, you go to a doctor. You wouldn't get the opinion of an architect before you appear before a judge and jury, you go to a lawyer. So don't go to a priest, or some random person on the internet for information about science. Not everyone's opinion is valid all of the time.