Alignments are just a guideline about how a creature generally behave. Only outsiders and some specific creatures are irremediably evil. And even then there are exceptions. What is truly important is what work at your table.
Lawful creature tend to favor an orderly and structured view/approach to problems or situations and interaction while a chaotic one will usually act on the spur of the moment, it's hunches and preferences with little or no regard to what others will think.
Good is good and evil is evil. Yet, good and evil changes from era to era as societies evolve. What we consider good today might be viewed as utterly evil by an other society. We all agree that a person is innocent until proven guilty. That is a good thing. But historically speaking, it is relatively new. It used to be guilty until proven otherwise. And it was the person that was wronged that would decide on the sentence (or its closest relatives). Was it a bad thing? In many ways, yes. But today, a lot of people are feeling that victims are left out by our system. People of ancient times would be appalled by seeing someone released because of insufficient proof and having a judge and not the victim deciding on the sentence. Ho, and woe to false accusers as they could be trialed for false accusations and suffer the fate they were trying to impose to their victims.
Such was the system in some ancient societies. Our system would seems evil to these people and what about people from the future? Would they see our system as an evil one too where the victims are left out and some criminals can go free?
So Alignments are very subjectives from one table to an other and from one society to an other. Do as you want at your table. Use the alignments for what they are, a subjective guideline to help you play the game you love regardless of what others might think.