A simple Google search shows that an opinion is "a view or judgement formed about something, not necessarily based on fact or knowledge." Everyone has an opinion, and opinions are ok to have. Opinions can be based on the available data (what you've read), or how you feel, or maybe a gut instinct. Opinions can be swayed based on what someone else says and whether or not you believe them. You can integrate your new knowledge into your personal database and your opinion may or may not change.
A scientific conclusion is backed up by data. There must be enough data to support the conclusion and conclusions can change based on the data available. This is why eggs were bad for us, then good, for us, then bad for us again. The scientific community is always producing more data, which can change the conclusion. The key here is that there is always data. Without data, it is not a scientific conclusion but rather it is an opinion.
Scientists can have opinions too, especially when we discuss "models." A scientific model is usually proposed when a scientist has some information about a process but there are holes. They often speculate on what might be happening with the idea that they will create experiements to fill in the holes and can and will change their model once they have additional data.
What is the problem with opinion and a scientific conclusion? Often, the general public gives as much validity to the opinion as they do to the scientific conclusion. In the world of the general public, an opinion weighs just as much as a scientific conclusion when the scientific conclusion should be given more weight.
There is a certain amount of trust in scientists needed for those members of the public that do not read or cannot understand the primary literature. Practice is needed to learn how to think critically about a study or article. THAT'S OK! It take time and practice. If you don't have the time or desire to read primary literature, that's ok too. Take a look at my previous post "Is it Fake" for ways to find good summaries or news articles on scientific studies.