"I have long since learnt that you cannot change people's opinions". I have to say, this comes down to the people involved - both the speaker and the listener.
If a person is of sufficient intellect to hold their own opinion whilst always keeping an open mind to other opinions and perspectives, in that instance there is a very real possibility that an opinion held can be changed.
Equally, the person sharing the opinion has to have the intellect to understand that it isn't just what they say which matters, but how it is delivered, the qualification behind it, and the authority of the person speaking to do so in the capacity which they are.
In other words (and I by no means attribute this to anyone specific in the world, let alone this forum; I speak quite generally here), if the person offering the opinion has no business to do so, and / or has not got the first clue what they are talking about, it is highly unlikely they are going to get anyone to changer their minds about a matter. Add to this poor tone, shouting, anger, and 101 other negative behaviours, leaves "the other" in even less state of wanting to listen to that opinion.
Of all the people I have met in my own life who were able to get me to reconsider a belief I was holding, it has always been those whose opinion was being sought, who knew their subject, could communicate it clearly and confidently, and not least were able to take a step back and not care too much whether or not I took on board their point of view.