An "opinion" that is clearly in opposition to a fact certainly has very little value, and I would consider it invalid. I'm not saying someone doesn't have the right to a useless, proven-wrong opinion, but the value of any of their words will be near-zero in my eyes.
Not all opinions are equal, not all opinions are valid or represent truth.
Some opinions may be purely subjective and not even involve any kind of truth or fact statement ("X tastes good") but those opinions have very little value overall. Not completely useless, but not far from it
I personally feel we're accelerating towards a future where little thought, time, effort, or trust is given to anything factual and opinion somehow is the holy grail (especially the tragic idea that all opinions are somehow on equal footing) and I think we'll be worse off for it