At the risk of over-simplification, I would wager that the most common human activity is distinction. What I mean by that of course is that we as humans see two things and we say "This is one thing, that is another." We make distinctions often without thinking about it. We can distinguish between two objects based on their physical quality, their quantity, their origin, their purpose or their relation to us.
For example, my first batch of french toast today burned, and so I fried up another batch (I promise though I did eat the first one too.) I acted in this way based on distinctions I made. I said "Here are two separate batches, one is burnt, one is not yet burnt, thus one and only one has the potential to be unburnt. The assumption I will make is that the burnt will be less tasty than the unburnt. Thus, I will make the second batch in the hopes of it being tastier and I will not leave the kitchen without making it." In many ways, the batches of french toast were the same. They were made in the same pan, they were both made to be eaten, and they were both made by me for me. Yet, because of the fact that they would be different, thus distinct, I made the choice, a distinct unique choice, to cook the second batch.
Another, perhaps more serious example, is what I have to do today. In the Notre Dame community, we call it DARTing, though it's really no more than registering for classes. I have 4 classes that I'm required to take for my major and one open slot (because I'm not going to overload). Because I have a choice for this last class, I have to make distinctions. I have to distinguish between a class that would interest me and one that would not, between a professor who I respect and one that I don't, or one I've never even heard of. My current plan is to take "The Age of Charlemagne" taught by Thomas Noble, a class that would interest me and a professor I respect.
We make these distinctions in our mind and make choices based on the distinctions. From this, we get actions that effect our world and ourselves. Looking at these actions, we make distinctions again, we say that they are either good or bad, virtuous or vicious. In other words, throughout our lives, we are constantly making judgements and without making them, we can not do anything. I could not write this blog post if I had not first decided that I wanted to and that I should, what topic it should cover, and that I should use "this" and not "that" (a real choice I made earlier in this post.)
Thus, judgements, whether judgements of quality, quantity, origin, purpose, or relation, are a normal and necessary part of our lives. So when we say that we should not judge the actions of ourselves and our fellow humans, we are fooling ourselves into thinking that we can live without such judgements, that we can just say "What I have done, I have done. There is nothing you can say of it."
And yet, we make these judgements, oftentimes, not in order to distinguish between what is a good action or a bad action, but in order to divide humanity, whether individuals, families, communities or countries. When we say that one person acts well and another acts wickedly, our natural (but not in any sense necessary) response is to reject the wicked person and welcome the good person. When we say that one family is a loving environment and one is dysfunctional, we wish to avoid the dysfunctional. When we say that one community is charitable and another is not, we wish to live in the one which is charitable. Thus, we set up dichotomies between persons, families and communities that set them against each other.
Now, it is not in any way to true that all people are equal in every way. We all have equal dignity before God and are all deserving of rights that result from this dignity. However it would be an equivocation to assert that that equal dignity meant that all humans were equal in every way. For example, some humans are less physically strong, others are less mentally strong. Some are more imaginative than others. Some are architects, some gymnasts, some teachers, some football players. These people are all different and have different strengths. In that sense they are not equal.
This inequality has many implications which I may go into later, but what it does not imply is a moral distinction. An architect is no more moral than a bricklayer, a teacher no more moral than a scientist, a theologian no more moral than a coal-miner. In fact, intellectual understanding of morals does not necessarily create a more moral life. Not only that, but an intellectual understanding of life does not make a more useful or productive or happy life.
The greatest problem, then, is when these inequalities, which are distinctions, are made the basis for judgements of quality, or moral judgements. All of us do bad things, and the distinctions between these actions and good actions are as I said necessary for the survival of humanity. However, less physical strength does not mean you are more or less likely to do bad things. Intellectual prowess does not either.
Thus we get divisions among humans, not because we have to keep our children away from sociopaths, but because we somehow think that the Lawyer is more respectable than a Carpenter. We set up the white collar against the blue collar. We set up intellectual against manual labor. We confuse distinction for division, and we suffer for it.