I can't get Calvinism

Could some Calvinist out there explain to me why someone can say with a peaceful mind, "True justice would be hell for the whole human race, wouldn't it?" (Source: "Calvinism, Arminianism, so what?" - but that's only one succinct statement of something which is widely believed by many.)

I can never quite understand how anyone can calmly believe that true justice requires that every human being who ever drew a single breath SHOULD suffer eternal conscious torment, that any exception to this rule is a miraculously gracious concession to which no human being could ever be entitled, and that the never-ending agony of each and every person ever born would be righteous and beautiful and perfect, and that we should joyfully worship the God who made it so.