A redated post.
Contrary to what you may have learned in grade school, the terms "fact" and "opinion" are far from clear. In order to have a fact, does it just need to be true or does it have to be provably true. Is there a "fact" about who committed an unsolved murder, even if we can't prove who did it one way or another. After all someone did commit the murder, right? In order to have an opinion, does that mean that it is neither true nor false, or both true and false depending on how you feel about it? Or is all you need for an opinion that it be open to controversy, in which case someone could have a correct opinion or an incorrect opinion (just not a provably correct or provably incorrect opinion).
We have a lot of social consensus about the wrongness of some actions. There was a controversy about whether O. J. killed Nicole and Ron, but no controversy about the rightness or the wrongness of the act of killing these two people. Is it "mere opinion" to say that slaughtering Nicole Brown Simpson and Ronald Goldman was wrong? Does it make sense to say that the only thing that was really wrong with it was that our social group disapproved of it?