right or wrong

why is always there a right thing and a wrong thing?
And why do we always have an option , even when we know that one of them is wrong . and why are we presented with the wrong option....that one knows that shouldn't be done.
At one point when people don't agree to a certain subject , they would say its my opinion and then its the end of topic. So if they see everything as an opinion why they have to label it as wrong or right.
I mean there are no set of rules by which one has to abide by (though i think life would have been much simpler with that).So why there is always a judgment that follows after anything one does. Why do people have to be critical of others. moreover why do one has to be critical of one own self.