Opinions are neither right nor wrong, they are simply ideas that people use to guide their life actions. To say that someone's opinion is right or wrong is using criteria from scientific reasoning to judge the "validity" of someone's thinking, and opinions fall outside of that. It would be like using cognitive science to "judge" whether Mozart was worth listening to, or if we should be listening to Iron Maiden or not. (As a side note, I think we are unfortunately moving into this kind of world.)
Let's take a look at some common opinions:
- Jesus is lord and savior.
- Paris is a romantic city.
- Buddhism is better than Christianity.
- Beethoven was a jerk.
- Science is the ultimate authority on Truth.
- Fiber is good for you.
- Citizen Kane is the best movie of all times
- UFOs are BS
- Chocolate Ice Cream (specifically Haagen Daaz) is the best ice cream.
It is tempting to look at each one of these statements and examine them with the light of reason and "prove" that they are right or wrong. "Obviously" Citizen Kane is the best movie of all times because all the critics who matter voted it best. "Obviously" Jesus is not lord and savior because there's no "proof" he existed. "Obviously" Jesus is lord and savior because he helped me win the State Finals. "Obviously" Beethoven was a jerk because he never smiled in any of his portraits and science says happy people smile. "Obviously" chocolate ice cream is the best because there are more sales of it so that "proves" that anyone who likes vanilla is "wrong." etc. etc.
As you can see, arguing opinions is like dancing on quick sand. They are personal ideas about the world and fall outside of the realm of reason / logic / right vs. wrong.
As amazing at it might be to some, there are many people who don't believe in scientific reasoning or some of its many axioms. We all think that the speed of light is a constant, so if anyone says that "in my opinion the speed of light is changing and is not a constant." people will look quite shocked. "What do you mean, opinion? It's a fact! We tested it, you ignoramous! It's 300,000m/s in a vacuum, like the one between your ears." Everyone who matters tested it and all agree, so your opinion is wrong. The group believes it, so your opinion is wrong. The authority administers truth so your opinion is wrong.
When do opinions change into "fact." What is a "fact" for that matter?
When you say "Vanilla is the best." The verb "is" makes this statement a fact and takes it outside the realm of opinion. However, it is difficult to speak English without using the word "is" when speaking about personal beliefs without sounding strange. This is why we preface statements with "In my opinion," an adverbial that modifies "is." So, I think it's better to say "In my opinion, Jesus is lord and savior." as this is less confrontational. Although some would argue that "in my opinion" here is an adjunct because of course the statement is true. We are all entitled to our opinions.