This is another very good essay, offering a clearly defined and well-supported view. The reasoning is crystal clear and the sentence structure is nicely varied, so it definitely merits a high score. Well done!
When writing an issue analysis, one helpful thing to look for: an opportunity to briefly explore the opposite viewpoint. Doing so will add to the persuasive power of your analysis by demonstrating that you have honestly considered both sides of the issue. In this case, you might devote a few sentences to discussing the recent gains in civil rights that have been achieved by people who resisted unjust laws:As you wrote in your essay: "The so-called 'just and unjust' is people's subjective opinion; thereby they fail to be taken as a standard to judge laws." That is certainly true, and you make a good point here. But keep in mind that the laws of a society are always written by human beings, and thus there is always the chance that subjectivity (biases, prejudices, etc.) will influence the law-making process, and that some of the society's laws will therefore be detrimental to the environment or to large groups of people.
But again, you've shown some very good writing skills, and should definitely get a high score on your essay.