I detest this attitude. None of us have any right whatsoever to wrong opinions. It's just that when the truth of a matter is vague people get away with being wrong because they're "innocent until proven guilty".
If Tybalt killed Stephen so he could get some inheritance money and then told everyone that in his opinion he had a right to do it, would anyone respect that? No, because the truth of the matter is very clear and he is obviously wrong.
Wrong opinions are like jaywalking. Lots of people do it, most of the time no harm is done and there are way worse problems to deal with. But when something really nasty happens and the guilty party tries the "everybody does it" argument, the correct response is: "Yes, and they shouldn't."