This is not allowed

Talking about what is allowed and what is not, is it still matter these days? I know a lot of people make mistakes when they are tempted to do something they should not do, -because of many different reasons such as morality, religious reason, self integrity, rule of law, etc. But making mistakes meaning they realize that it is not a right thing to do, that there is a rule they violate, or standard they do not adhere to, a ruler they jump over. That's a different story. But when they have no idea what they do, and others tell them that they do something wrong, the normal reaction is, usually, they will ask 'But why not?'. That is the problem: these two people have different set of standard. A's standard is 1,2,3, while B's standard is 4,5,6. They will go side by side but literally they will never meet at any point in time because they are like two parallel lines, there's no way that they will meet. Somehow, the experience I've just encountered reflected this illustration. No details provided, but when I tried to remind, say, M, that it was not allowed, this person asked me back, 'But why not? What's wrong with that?'. Then I know right away that we don't have the same set of standard. I walked the other line, and that person just walked another parallel line. We might say hi to each other, but we will never stop at the same point. So I said adieu.