"Everyone has and is allowed to have their own opinion. However, whenever fact enters the playing field, opinion is rendered irrelevant and must bow to fact. Opinion only matters with regard to likes and dislikes; e.g., what the best colour in the world is. Opinion is merely personal preference and is no contender against fact." —Me
The next time someone tries arguing that something is just "your opinion," remember my above words. Opinion is merely personal preference and only matters in the realm of personal likes and dislikes; where a thing cannot possibly be proven. I like the colour blue, and so it is very much my opinion when I say that blue is the greatest colour in the world, because it cannot be proven in the least. Someone else will say red is the greatest colour in the world, and that is their opinion. Opinions are not things with which to fight about; they are not hills to die on!
I could say apples are the best fruit in the world and someone else could say that oranges are. Now, if we were arguing about which is the healthiest fruit, we could indeed determine through science which fruit truly is the healthiest. Doing so would be introducing fact, which would make any opinion on what the healthiest fruit is irrelevant. But in regard to what you or I consider to be the best fruit (based solely on what we prefer over all the others), they are just opinions.
With that said, opinions are personal preferences but personal preferences are not opinions—especially where morality and what is right and wrong are concerned. I might prefer to use a quarterstaff to a gun, but preferring the one over the other is not an opinion. Saying that one is better than the other is an opinion, unless why you are saying it is better is qualified (e.g., it is better for killing, it is better for hunting, it is better for self-defense).
Opinion has nothing to do with biblical interpretation, so someone arguing "That's your interpretation" is merely attempting to use it as a synonym for "That's your opinion." My interpretation can either be right or it can be wrong! It cannot be treated as though it is merely an opinion, because it is not!
Too many people are tossing the phrase "That's your opinion" around, ignorant as to what an opinion actually is, attempting to re-define the word "opinion." That is one of the things that irritates me the most about post-modern society. Everyone is ignorant of the fact that words have meanings, and they attempt to re-define just about every word they use. Thus, for every individual, all these words mean different things. It makes communicating difficult, if not impossible. When you learn about amelioration (words that used to have negative meanings but now have positive meanings), pejoration (words that used to have positive meanings but now have negative meanings), and contronyms (also spelled contranyms; words that have contradictory meanings), you really understand why English is the most difficult language in the world to learn. As an example, the word "brave" use to mean something negative, pretty much the opposite of what it means to us today. It makes you wonder about those who have picked up ancient books and read them, understanding the words they used by the definitions we have today. Words like unicorn. I mean, what will post-modern children think of when they are watching The Flintstones and in the theme song they hear, "We'll have a gay old time"? What about when they see the title of the movie The Gay Divorcee?
If ignorance is bliss, then most of these people must be living in paradise. Learn what an opinion is and quit using the word incorrectly!