Jack Campin.... I could not resist peeking at Crazy Gail's pages. I had to tear myself away.....scary!

What immediately popped into my head was the philosophical/logical principle: "From false premises, anything follows." The point is, it doesn't require that anyone be as crazy as Gail, or follow such extreme flights of fancy. All that is required is to adopt one or two beliefs that cannot be substantiated, and they can then proceed to entire systems of thought & action that are thus by definition merely 'opinion'. In some cases, these are benign and harmless, but sometimes they lead to activities dangerous to society.
   George Zimmerman had certain beliefs that led him to act in ways that led to the death of Trayvon Martin. He probably still 'believes' that his actions were 'justified', even if they didn't turn out the way he hoped.