I'll tread as lightly as possible with this one since I don't mean to upset anyone.
The problem with this is that what is real or not is also an opinion. So discussing opinions is pretty silly, instead you can discuss reasonings and theories.
There is a distinct difference between an opinion (that which I accept as to be true) and a reasoning (that which is why I accept something to be true).
In your example "unicorns suck" is the opinion, the reasoning is different and you can discuss that.
And that's why this entire discussion is a bit silly.
People give a reasoning and then later say that it's an opinion.