Opinion or Fact? Whose to say there not the same

Recently, I was at school and was confronted on a certain contraversial view. A classmate of mine decided to disagree with my teacher on a certain law only used in a few states. The student said it should be outlawed, and the teacher said it should not. They argued for awhile both making very distinguished points on the issue. But while listening I couldnt sit and not question some of the so called "facts" they were proposing. But then I thought to myself, who am I to say what is a fact and what is a an opinion? Why should anyone be allowed to hear one persons view and say it isn't correct. Even if it isn't right doesnt mean it's not a fact, when it very well may be. The technical definition of opinion is "the expression of a belief that is held with confidence but not substantiated by positive knowledge or proof". But then again, who is to say what is positive knowledge or proof. Sure we know for an opinion to be true it should have something supporting it. But for example I'm willing to bet the first person that suggested we should bury the dead, was critcized by his peers. Saying it was inadequate or not proper. But his opinion became more well known, and is now supported by a vast majority of the entire human population. So we then decided to find facts to support his opinion also, such as the cadaver is sickening and shouldnt be in sight. So I guess what i'm trying to say is don't take somones opinion and say it can't be possible or will never come to be. Because there may very well be facts that support it, but no one has took the time to search. So be respectful of opinions because they are the base and ground of where facts came from.