Answer and Explanation:
Well, how is any opinion formed?
Your own thoughts and experiences.
2. Marketing and media
3. Opinions/experiences of friends
4. Opinions/experiences of authorities (parents, teacher, governmental, legal, etc.)
Depending on the individual (and public opinion is simply a composite of individual opinions) the weight for each of the factors listed above differ.
When I was in my teens, the opinion of authorities was heavily weighed. I did not have sufficient experience to make good judgements.
In my 20s, my own thoughts and experiences (and those of my friends) was important, because I was gaining the experiences to formulated my own opinions.
Marketing really strives to form your opinion for you. If they can get you to believe that X is valuable, then they make more money. Warning: always listen to all sides. You do not want someone to control your opinion.
I am now in my 60s, and have sufficient experience to formulate my own opinions. I am hard to classify, because my personal experiences differ from anyone else’s.