'Opinions' might be a little strong, but when you already have a clue about the topic in question, forming a hypothesis before testing its validity can work better than randomly 'throwing shit against the wall to see what sticks'.

Your criteria for what constitutes valid evidence are also critical to formulating an evidence-based opinion that matches actual reality. Look at the climate fakery, for example. Look at election 'results'. Look at Putin's 'unprovoked' attack. Look at the 'female penis', or rather, don't. Going by found-evidence alone can turn the credulous person into a MIC puppet in a fantasy world.

However you arrive at your opinion, it should be verified by testing your evidence against as much actual reality as you can uncover. Unless you're doing hard science though, at the end of the day it's still often a judgement call.