Just a remark: Not everything that "has no objective reality" (read: material basis) is an illusion or a lie. Even if we ignore the pesky nagging question whether objective reality exists and if yes, how we might determine it. Or the eye-rolling physicists who discovered a hundred years ago that what we think of as solid, deterministic matter (and hence reality) is all one fuzzy non-deterministic entangled heap of writhing, glowing spaghetti that's best left alone.

As I recall Hugh Gibbons, my professor of Legal Philosophy, passed away in 2017. He posted some papers on Biology of Law. This 26 page paper by Hugh presents his view that the (legitimate) purpose of law is the institutional or government intent to expand freedom for individuals in society: biologyoflaw.org/Purpose/PurposeLaw.pdf. The terms defined in the Appendix might be read first and consulted while reading the paper. Hugh regards the law, paradoxically, as a means to expand freedom of individuals in society by using public coercion to influence incentives of private agents.

Morality and justice is all about the knowledge of good and bad, and if morality is meaningless, then what is meaningful without such knowledge?...

Actually morals and justice are objective, just because there is not universal agreement on what they are does not mean there are no objective morals.

Can we get a split for this question? Justice underwent a paradigm shift in the prior century, and we now have an entire field of game theory, fair division, which mathematically describes justice but not morality.

"if they agreed on the axioms." One of the axioms of ZF (ZF is probably the most commonly used axiomatic basis for mathematics these days) is "Every non-empty set $x$ contains a member $y$ such that $x$ and $y$ are disjoint sets." Would you say that you agree with this statement? In the early 20th century, there was actually much disagreement about a satisfactory set of axioms for mathematics. My point here hasn't to do with ZF, but merely to point out that perhaps "agreeing on the axioms" is not as simple an ask as you make it out to be.

@Him why $ $ don't make latex ? and I mean if we agreed on the axioms then we will not disagree on results

"I like to compare everything to Pure Mathematics" this is an error. Notably, basically all of science is not axiomatic in nature. Physics may feel axiomatic because you learned about "fundamental laws" in school, but those fundamental laws aren't axioms, they are observations about the world. Just because gravity isn't an axiom, doesn't mean it's not objective. Perhaps, a better view is that morality and justice are not mathematical theorems to be proved, but as social phenomena that occur and that need to be observed in order to be understood.

@Him I know that, This was the biggest reason on why I chose to study mathematics , When I was in high school I liked reading but I avoided reading any non mathematical book because topics like history, philosophy etc are greatly influenced with believes, religion etc and I cannot be sure of any of those . The idea that in every non mathematical there is opinion and apposite opinion and to reach to the truth you had to dig up in 10000 books that made me hate any non mathematical book. This is my problem from +4 years and still to this day I think everything should be a math theorem

"opinion vs opinion" perhaps. And yet, even when all is opinion, there are yet facts. For example, the statement "It is my opinion that there are no just wars" is either true or false. That either is my opinion, or it is not. In this sense, one can understand the facts of morality and justice precisely by understanding the complement and contrast of the many opinions about same. Certainly any judgement about anyone's opinion first requires the comprehension of the fact that they opine. Such observations could certainly fill a lifetime before getting around to having opinions of one's own.

"What do philosophers think about them?" I'll care what philosophers think when they do something productive, like digging a ditch.

I hate to tell you this, but there's plenty of philosophical argument to be had within mathematics itself too. That's the entire reason Philosophy of Mathematics exists. For one pretty prominent example, there are those who reject the validity of the law of the excluded middle, and so wouldn't necessarily come to the same conclusions given a set of axioms than those who accept it.

@JustinHilyard well as someone who is still a beginner I never heard of this before

Your title question is whether justice is meaningless. Your body asks about its rigorous definition. V v different: If say your beloved better half (spouse, gf... etc) is very beautiful, you may not be able to define her beauty, leave aside rigorously, but that doesn't make the beauty meaningless. So which is the question?

@Rushi BTw I think Beauty, art , etc to be as meaningless for me as justice or any thing that has a non rigorous definition, unlike beauty the definition of morals and justice affect our lives a lot one can be dead because of these and another is willing to die and kill because of these so Beauty for me is not important and I think we need rigorous system of morals

Your comment above is more self contradictory than you realize. You say beauty doesnt matter, whereas your life does. What if, say, there is strong statistical evidence that people who like a certain kind of music are significantly more likely to commit a violent crime than people who like another kind? What if the second kind is generally considered to be more beautiful. But not more rigorously?? I recommend a careful study of (this) Jordan Peterson

@Rushi That is a good point but what I meant is that Beauty doesn't matter (much) in comparison to morals or justice

You're repeating yourself: Imagine you have chronic headaches. The doctor suggests you visit an optometrist. And you respond with I'm not going to an optometrist, I have a headache not an eye ache!

@Rushi I am missing the point here what does that have to do with mathematics ?

@ScottRowe Dunno if you're being (quasi) ironic. But replace 'Bach' by 'Mozart' and you get a real thing.

I think, from Absolute Knowledge of view, Ethics meaning is beginning or birth and Morality meaning is end or death. Thinking about that, I wrote an article regarding "everything, nothing and neither so" Sharing as is, maybe interested.

"mathematics is the closest thing to absolute truth" And yet, being entirely a construct of the human mind, it turns out to be exactly the opposite. "if they agreed on the axioms" That's exactly the part why it's not absolute.

Could you re-phrase at least the exposition, if not the Question itself? Does the fact that every child can ask 'What do philosophers think of (thisthat)?' make the Question worthy of serious consideration? Other beliefs are available and mine is that all Quoran Questions should take the four-part form: Statement, support, contradiction, query 1) The world is flat. 2) I see that on land, but from a ship approaching land the idea seems less realistic. 3) From a ship at sea, the land seems to rise up from the horizon. 4) Since, the land cannot 'rise up' what is really happening?