Why is the declaration of independence still used today as the basis of aruguments? is it a moral judgement? is so can you expand on that?

The Declaration of Independence is still used as an argument today because it makes several statements about equality and morality that are the basis for much of modern society. The section that most people will remember, the part that states that all people deserve life, liberty, and the pursuit of happiness is still applicable today.

Just to list an example of one way that the Declaration of Independence can be used as an argument, the aforementioned section can easily be used to justify equality. If everyone deserves to be able to live happily, doesn't that mean everyone, including people of different genders, races, and nationalities? This excerpt is from Martin Luther King Jr.'s famous "I Have a Dream" speech:
"In a sense we have come to our nation's capital to cash a check. When the architects of our republic wrote the magnificent words of the Constitution and the Declaration of Independence, they were signing a promissory note to which every American was to fall heir. This note was a promise that all men, yes, black men as well as white men, would be guaranteed the unalienable rights of life, liberty, and the pursuit of happiness."

The Declaration of Independence can be used as a moral argument. Morally, most Americans believe that everyone deserves the same rights and treatment regardless of their background. It cannot be objectively stated that everyone deserves the same chance at life, liberty, and the pursuit of happiness, but most people will agree that this is true because of their morals.

Hope this helps!