"What is the point of making out your family tree? What are you trying to prove? Are you implying you are superior or something?" These are valid questions that occur to people when they see family trees. And they are not helped by the snobbery and wishful-thinking of many who do engage in the pursuit.
Other people complain that proving someone descends from, say, Edward III through a long chain of people is meaningless - not only will they not have inherited a single piece of property, papers, or even the vaguest family stories, attitudes or behaviour from him, but they may not have even inherited a single gene from him. e.g. See [Kingman, 1999] for this type of criticism.
I thought I'd write a few words in defence of genealogy.
We know very well that we need a lot of generations to get from 1720 to 1950. Genealogy reminds us that we need exactly the same number of generations to get from 1220 to 1450. It forces us to pick our way step by step through those long unchanging medieval years.
You can imagine what a real, step-by-step genealogy of the last 5 million years (since divergence from our last common ancestor with any other living species) would look like. With page after page of tedious progression, it would be a lot more eloquent than simply trying to explain large numbers.
And in fact, while most genealogy is meaningless but precise, the overall patterns do have meaning. For example, my Royal Descents of famous people list is slowly building up a vivid illustration of how interconnected the world really is, and how in a sense all tribes and nations are fictional constructs. It is vivid because it actually puts names on people, and shows every step of the way how blood from any source, no matter how supposedly "elite", can end up years later in almost any destination at all.
This is especially true when applied to the nobility and royalty, who are often the only ancestors you are left with in the more distant past. Why should you admire some noble, or take their side, just because you descend from them? The nobility of the past were often no more than the most successful robbers, stealing other people's land, and living off other people's work. They weren't Appointed By God, but were the survivors of a long process of selection among the most aggressive and best-organised Strong Men, aided by the greatest thieves of them all, the Royal family.
No, the desire for a Royal Descent is quite different. It's because most of us exist in little islands of peasants and farmers, interconnected to each other but to no one else, and for all we know we would still exist no matter what had happened in mainstream history in the big world outside. And the only way to break out of this island is to find a connection to one of these Strong Men, after which things explode and history becomes full of events on which our existence provably depends. The peer, the heiress, the gent, the precious link to the World Family Tree, is your goal, but to expect to actually like him or her, or be proud of them, is to rather miss the point.